open-vault/builtin/logical/pki/crl_util.go

package pki

import (
	"bytes"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"fmt"
	"math/big"
	"strings"
	"sync"
	"time"

	atomic2 "go.uber.org/atomic"

	"github.com/hashicorp/vault/sdk/helper/certutil"
	"github.com/hashicorp/vault/sdk/helper/consts"
	"github.com/hashicorp/vault/sdk/helper/errutil"
	"github.com/hashicorp/vault/sdk/logical"
)

const (
	revokedPath                      = "revoked/"
	crossRevocationPrefix            = "cross-revocation-queue/"
	crossRevocationPath              = crossRevocationPrefix + "{{clusterId}}/"
	deltaWALLastBuildSerialName      = "last-build-serial"
	deltaWALLastRevokedSerialName    = "last-revoked-serial"
	localDeltaWALPath                = "delta-wal/"
	localDeltaWALLastBuildSerial     = localDeltaWALPath + deltaWALLastBuildSerialName
	localDeltaWALLastRevokedSerial   = localDeltaWALPath + deltaWALLastRevokedSerialName
	unifiedDeltaWALPrefix            = "unified-delta-wal/"
	unifiedDeltaWALPath              = "unified-delta-wal/{{clusterId}}/"
	unifiedDeltaWALLastBuildSerial   = unifiedDeltaWALPath + deltaWALLastBuildSerialName
	unifiedDeltaWALLastRevokedSerial = unifiedDeltaWALPath + deltaWALLastRevokedSerialName
)

type revocationInfo struct {
	CertificateBytes  []byte    `json:"certificate_bytes"`
	RevocationTime    int64     `json:"revocation_time"`
	RevocationTimeUTC time.Time `json:"revocation_time_utc"`
	CertificateIssuer issuerID  `json:"issuer_id"`
}

type revocationRequest struct {
	RequestedAt time.Time `json:"requested_at"`
}

type revocationConfirmed struct {
	RevokedAt string `json:"revoked_at"`
	Source    string `json:"source"`
}

type revocationQueueEntry struct {
	Cluster string
	Serial  string
}

type (
	// Placeholder in case of migrations needing more data. Currently
	// we use the path name to store the serial number that was revoked.
	deltaWALInfo struct{}
	lastWALInfo  struct {
		// Info to write about the last WAL entry. This is the serial number
		// of the last revoked certificate.
		//
		// We write this below in revokedCert(...) and read it in
		// rebuildDeltaCRLsIfForced(...).
		Serial string `json:"serial"`
	}
	lastDeltaInfo struct {
		// Info to write about the last built delta CRL. This is the serial
		// number of the last revoked certificate that we saw prior to delta
		// CRL building.
		//
		// We write this below in buildAnyCRLs(...) and read it in
		// rebuildDeltaCRLsIfForced(...).
		Serial string `json:"serial"`
	}
)

// crlBuilder is gatekeeper for controlling various read/write operations to the storage of the CRL.
// The extra complexity arises from secondary performance clusters seeing various writes to its storage
// without the actual API calls. During the storage invalidation process, we do not have the required state
// to actually rebuild the CRLs, so we need to schedule it in a deferred fashion. This allows either
// read or write calls to perform the operation if required, or have the flag reset upon a write operation
//
// The CRL builder also tracks the revocation configuration.
type crlBuilder struct {
	_builder              sync.Mutex
	forceRebuild          *atomic2.Bool
	canRebuild            bool
	lastDeltaRebuildCheck time.Time

	_config               sync.RWMutex
	dirty                 *atomic2.Bool
	config                crlConfig
	haveInitializedConfig bool

	// Whether to invalidate our LastModifiedTime due to write on the
	// global issuance config.
	invalidate *atomic2.Bool

	// Global revocation queue entries get accepted by the invalidate func
	// and passed to the crlBuilder for processing.
	haveInitializedQueue *atomic2.Bool
	revQueue             *revocationQueue
	removalQueue         *revocationQueue
	crossQueue           *revocationQueue
}

const (
	_ignoreForceFlag  = true
	_enforceForceFlag = false
)

func newCRLBuilder(canRebuild bool) *crlBuilder {
	return &crlBuilder{
		forceRebuild: atomic2.NewBool(false),
		canRebuild:   canRebuild,
		// Set the last delta rebuild window to now, delaying the first delta
		// rebuild by the first rebuild period to give us some time on startup
		// to stabilize.
		lastDeltaRebuildCheck: time.Now(),
		dirty:                 atomic2.NewBool(true),
		config:                defaultCrlConfig,
		invalidate:            atomic2.NewBool(false),
		haveInitializedQueue:  atomic2.NewBool(false),
		revQueue:              newRevocationQueue(),
		removalQueue:          newRevocationQueue(),
		crossQueue:            newRevocationQueue(),
	}
}

func (cb *crlBuilder) markConfigDirty() {
	cb.dirty.Store(true)
}

func (cb *crlBuilder) reloadConfigIfRequired(sc *storageContext) error {
	if cb.dirty.Load() {
		// Acquire a write lock.
		cb._config.Lock()
		defer cb._config.Unlock()

		if !cb.dirty.Load() {
			// Someone else might've been reloading the config; no need
			// to do it twice.
			return nil
		}

		config, err := sc.getRevocationConfig()
		if err != nil {
			return err
		}

		previousConfig := cb.config

		// Set the default config if none was returned to us.
		if config != nil {
			cb.config = *config
		} else {
			cb.config = defaultCrlConfig
		}

		// Updated the config; unset dirty.
		cb.dirty.Store(false)
		triggerChangeNotification := true
		if !cb.haveInitializedConfig {
			cb.haveInitializedConfig = true
			triggerChangeNotification = false // do not trigger on the initial loading of configuration.
		}

		// Certain things need to be triggered on all server types when crlConfig is loaded.
		if triggerChangeNotification {
			cb.notifyOnConfigChange(sc, previousConfig, cb.config)
		}
	}

	return nil
}

func (cb *crlBuilder) notifyOnConfigChange(sc *storageContext, priorConfig crlConfig, newConfig crlConfig) {
	// If you need to hook into a CRL configuration change across different server types
	// such as primary clusters as well as performance replicas, it is easier to do here than
	// in two places (API layer and in invalidateFunc)
	if priorConfig.UnifiedCRL != newConfig.UnifiedCRL && newConfig.UnifiedCRL {
		sc.Backend.unifiedTransferStatus.forceRun()
	}

	if priorConfig.UseGlobalQueue != newConfig.UseGlobalQueue && newConfig.UseGlobalQueue {
		cb.haveInitializedQueue.Store(false)
	}
}

func (cb *crlBuilder) getConfigWithUpdate(sc *storageContext) (*crlConfig, error) {
	// Config may mutate immediately after accessing, but will be freshly
	// fetched if necessary.
	if err := cb.reloadConfigIfRequired(sc); err != nil {
		return nil, err
	}

	cb._config.RLock()
	defer cb._config.RUnlock()

	configCopy := cb.config
	return &configCopy, nil
}

func (cb *crlBuilder) checkForAutoRebuild(sc *storageContext) error {
	cfg, err := cb.getConfigWithUpdate(sc)
	if err != nil {
		return err
	}

	if cfg.Disable || !cfg.AutoRebuild || cb.forceRebuild.Load() {
		// Not enabled, not on auto-rebuilder, or we're already scheduled to
		// rebuild so there's no point to interrogate CRL values...
		return nil
	}

	// Auto-Rebuild is enabled. We need to check each issuer's CRL and see
	// if its about to expire. If it is, we've gotta rebuild it (and well,
	// every other CRL since we don't have a fine-toothed rebuilder).
	//
	// We store a list of all (unique) CRLs in the cluster-local CRL
	// configuration along with their expiration dates.
	internalCRLConfig, err := sc.getLocalCRLConfig()
	if err != nil {
		return fmt.Errorf("error checking for auto-rebuild status: unable to fetch cluster-local CRL configuration: %w", err)
	}

	// If there's no config, assume we've gotta rebuild it to get this
	// information.
	if internalCRLConfig == nil {
		cb.forceRebuild.Store(true)
		return nil
	}

	// If the map is empty, assume we need to upgrade and schedule a
	// rebuild.
	if len(internalCRLConfig.CRLExpirationMap) == 0 {
		cb.forceRebuild.Store(true)
		return nil
	}

	// Otherwise, check CRL's expirations and see if its zero or within
	// the grace period and act accordingly.
	now := time.Now()

	period, err := time.ParseDuration(cfg.AutoRebuildGracePeriod)
	if err != nil {
		// This may occur if the duration is empty; in that case
		// assume the default. The default should be valid and shouldn't
		// error.
		defaultPeriod, defaultErr := time.ParseDuration(defaultCrlConfig.AutoRebuildGracePeriod)
		if defaultErr != nil {
			return fmt.Errorf("error checking for auto-rebuild status: unable to parse duration from both config's grace period (%v) and default grace period (%v):\n- config: %v\n- default: %w\n", cfg.AutoRebuildGracePeriod, defaultCrlConfig.AutoRebuildGracePeriod, err, defaultErr)
		}

		period = defaultPeriod
	}

	for _, value := range internalCRLConfig.CRLExpirationMap {
		if value.IsZero() || now.After(value.Add(-1*period)) {
			cb.forceRebuild.Store(true)
			return nil
		}
	}

	return nil
}

// Mark the internal LastModifiedTime tracker invalid.
func (cb *crlBuilder) invalidateCRLBuildTime() {
	cb.invalidate.Store(true)
}

// Update the config to mark the modified CRL. See note in
// updateDefaultIssuerId about why this is necessary.
func (cb *crlBuilder) flushCRLBuildTimeInvalidation(sc *storageContext) error {
	if cb.invalidate.CAS(true, false) {
		// Flush out our invalidation.
		cfg, err := sc.getLocalCRLConfig()
		if err != nil {
			cb.invalidate.Store(true)
			return fmt.Errorf("unable to update local CRL config's modification time: error fetching: %w", err)
		}

		cfg.LastModified = time.Now().UTC()
		cfg.DeltaLastModified = time.Now().UTC()
		err = sc.setLocalCRLConfig(cfg)
		if err != nil {
			cb.invalidate.Store(true)
			return fmt.Errorf("unable to update local CRL config's modification time: error persisting: %w", err)
		}
	}

	return nil
}

// rebuildIfForced is to be called by readers or periodic functions that might need to trigger
// a refresh of the CRL before the read occurs.
func (cb *crlBuilder) rebuildIfForced(sc *storageContext) error {
	if cb.forceRebuild.Load() {
		return cb._doRebuild(sc, true, _enforceForceFlag)
	}

	return nil
}

// rebuild is to be called by various write apis that know the CRL is to be updated and can be now.
func (cb *crlBuilder) rebuild(sc *storageContext, forceNew bool) error {
	return cb._doRebuild(sc, forceNew, _ignoreForceFlag)
}

// requestRebuildIfActiveNode will schedule a rebuild of the CRL from the next read or write api call assuming we are the active node of a cluster
func (cb *crlBuilder) requestRebuildIfActiveNode(b *backend) {
	// Only schedule us on active nodes, as the active node is the only node that can rebuild/write the CRL.
	// Note 1: The CRL is cluster specific, so this does need to run on the active node of a performance secondary cluster.
	// Note 2: This is called by the storage invalidation function, so it should not block.
	if !cb.canRebuild {
		b.Logger().Debug("Ignoring request to schedule a CRL rebuild, not on active node.")
		return
	}

	b.Logger().Info("Scheduling PKI CRL rebuild.")
	// Set the flag to 1, we don't care if we aren't the ones that actually swap it to 1.
	cb.forceRebuild.Store(true)
}

func (cb *crlBuilder) _doRebuild(sc *storageContext, forceNew bool, ignoreForceFlag bool) error {
	cb._builder.Lock()
	defer cb._builder.Unlock()
	// Re-read the lock in case someone beat us to the punch between the previous load op.
	forceBuildFlag := cb.forceRebuild.Load()
	if forceBuildFlag || ignoreForceFlag {
		// Reset our original flag back to 0 before we start the rebuilding. This may lead to another round of
		// CRL building, but we want to avoid the race condition caused by clearing the flag after we completed (An
		// update/revocation occurred attempting to set the flag, after we listed the certs but before we wrote
		// the CRL, so we missed the update and cleared the flag.)
		cb.forceRebuild.Store(false)

		// if forceRebuild was requested, that should force a complete rebuild even if requested not too by forceNew
		myForceNew := forceBuildFlag || forceNew
		return buildCRLs(sc, myForceNew)
	}

	return nil
}

func (cb *crlBuilder) _getPresentDeltaWALForClearing(sc *storageContext, path string) ([]string, error) {
	// Clearing of the delta WAL occurs after a new complete CRL has been built.
	walSerials, err := sc.Storage.List(sc.Context, path)
	if err != nil {
		return nil, fmt.Errorf("error fetching list of delta WAL certificates to clear: %s", err)
	}

	// We _should_ remove the special WAL entries here, but we don't really
	// want to traverse the list again (and also below in clearDeltaWAL). So
	// trust the latter does the right thing.
	return walSerials, nil
}

func (cb *crlBuilder) getPresentLocalDeltaWALForClearing(sc *storageContext) ([]string, error) {
	return cb._getPresentDeltaWALForClearing(sc, localDeltaWALPath)
}

func (cb *crlBuilder) getPresentUnifiedDeltaWALForClearing(sc *storageContext) ([]string, error) {
	return cb._getPresentDeltaWALForClearing(sc, unifiedDeltaWALPath)
}

func (cb *crlBuilder) _clearDeltaWAL(sc *storageContext, walSerials []string, path string) error {
	// Clearing of the delta WAL occurs after a new complete CRL has been built.
	for _, serial := range walSerials {
		// Don't remove our special entries!
		if strings.HasSuffix(serial, deltaWALLastBuildSerialName) || strings.HasSuffix(serial, deltaWALLastRevokedSerialName) {
			continue
		}

		if err := sc.Storage.Delete(sc.Context, path+serial); err != nil {
			return fmt.Errorf("error clearing delta WAL certificate: %s", err)
		}
	}

	return nil
}

func (cb *crlBuilder) clearLocalDeltaWAL(sc *storageContext, walSerials []string) error {
	return cb._clearDeltaWAL(sc, walSerials, localDeltaWALPath)
}

func (cb *crlBuilder) clearUnifiedDeltaWAL(sc *storageContext, walSerials []string) error {
	return cb._clearDeltaWAL(sc, walSerials, unifiedDeltaWALPrefix)
}

func (cb *crlBuilder) rebuildDeltaCRLsIfForced(sc *storageContext, override bool) error {
	// Delta CRLs use the same expiry duration as the complete CRL. Because
	// we always rebuild the complete CRL and then the delta CRL, we can
	// be assured that the delta CRL always expires after a complete CRL,
	// and that rebuilding the complete CRL will trigger a fresh delta CRL
	// build of its own.
	//
	// This guarantee means we can avoid checking delta CRL expiry. Thus,
	// we only need to rebuild the delta CRL when we have new revocations,
	// within our time window for updating it.
	cfg, err := cb.getConfigWithUpdate(sc)
	if err != nil {
		return err
	}

	if !cfg.EnableDelta {
		// We explicitly do not update the last check time here, as we
		// want to persist the last rebuild window if it hasn't been set.
		return nil
	}

	deltaRebuildDuration, err := time.ParseDuration(cfg.DeltaRebuildInterval)
	if err != nil {
		return err
	}

	// Acquire CRL building locks before we get too much further.
	cb._builder.Lock()
	defer cb._builder.Unlock()

	// Last is setup during newCRLBuilder(...), so we don't need to deal with
	// a zero condition.
	now := time.Now()
	last := cb.lastDeltaRebuildCheck
	nextRebuildCheck := last.Add(deltaRebuildDuration)
	if !override && now.Before(nextRebuildCheck) {
		// If we're still before the time of our next rebuild check, we can
		// safely return here even if we have certs. We'll wait for a bit,
		// retrigger this check, and then do the rebuild.
		return nil
	}

	// Update our check time. If we bail out below (due to storage errors
	// or whatever), we'll delay the next CRL check (hopefully allowing
	// things to stabilize). Otherwise, we might not build a new Delta CRL
	// until our next complete CRL build.
	cb.lastDeltaRebuildCheck = now

	rebuildLocal, err := cb._shouldRebuildLocalCRLs(sc, override)
	if err != nil {
		return err
	}

	rebuildUnified, err := cb._shouldRebuildUnifiedCRLs(sc, override)
	if err != nil {
		return err
	}

	if !rebuildLocal && !rebuildUnified {
		return nil
	}

	// Finally, we must've needed to do the rebuild. Execute!
	return cb.rebuildDeltaCRLsHoldingLock(sc, false)
}

func (cb *crlBuilder) _shouldRebuildLocalCRLs(sc *storageContext, override bool) (bool, error) {
	// Fetch two storage entries to see if we actually need to do this
	// rebuild, given we're within the window.
	lastWALEntry, err := sc.Storage.Get(sc.Context, localDeltaWALLastRevokedSerial)
	if err != nil || !override && (lastWALEntry == nil || lastWALEntry.Value == nil) {
		// If this entry does not exist, we don't need to rebuild the
		// delta WAL due to the expiration assumption above. There must
		// not have been any new revocations. Since err should be nil
		// in this case, we can safely return it.
		return false, err
	}

	lastBuildEntry, err := sc.Storage.Get(sc.Context, localDeltaWALLastBuildSerial)
	if err != nil {
		return false, err
	}

	if !override && lastBuildEntry != nil && lastBuildEntry.Value != nil {
		// If the last build entry doesn't exist, we still want to build a
		// new delta WAL, since this could be our very first time doing so.
		//
		// Otherwise, here, now that we know it exists, we want to check this
		// value against the other value. Since we previously guarded the WAL
		// entry being non-empty, we're good to decode everything within this
		// guard.
		var walInfo lastWALInfo
		if err := lastWALEntry.DecodeJSON(&walInfo); err != nil {
			return false, err
		}

		var deltaInfo lastDeltaInfo
		if err := lastBuildEntry.DecodeJSON(&deltaInfo); err != nil {
			return false, err
		}

		// Here, everything decoded properly and we know that no new certs
		// have been revoked since we built this last delta CRL. We can exit
		// without rebuilding then.
		if walInfo.Serial == deltaInfo.Serial {
			return false, nil
		}
	}

	return true, nil
}

func (cb *crlBuilder) _shouldRebuildUnifiedCRLs(sc *storageContext, override bool) (bool, error) {
	// Unified CRL can only be built by the main cluster.
	b := sc.Backend
	if b.System().ReplicationState().HasState(consts.ReplicationDRSecondary|consts.ReplicationPerformanceStandby) ||
		(!b.System().LocalMount() && b.System().ReplicationState().HasState(consts.ReplicationPerformanceSecondary)) {
		return false, nil
	}

	// Fetch two storage entries to see if we actually need to do this
	// rebuild, given we're within the window.
	lastWALEntry, err := sc.Storage.Get(sc.Context, unifiedDeltaWALLastRevokedSerial)
	if err != nil || !override && (lastWALEntry == nil || lastWALEntry.Value == nil) {
		// If this entry does not exist, we don't need to rebuild the
		// delta WAL due to the expiration assumption above. There must
		// not have been any new revocations. Since err should be nil
		// in this case, we can safely return it.
		return false, err
	}

	lastBuildEntry, err := sc.Storage.Get(sc.Context, unifiedDeltaWALLastBuildSerial)
	if err != nil {
		return false, err
	}

	if !override && lastBuildEntry != nil && lastBuildEntry.Value != nil {
		// If the last build entry doesn't exist, we still want to build a
		// new delta WAL, since this could be our very first time doing so.
		//
		// Otherwise, here, now that we know it exists, we want to check this
		// value against the other value. Since we previously guarded the WAL
		// entry being non-empty, we're good to decode everything within this
		// guard.
		var walInfo lastWALInfo
		if err := lastWALEntry.DecodeJSON(&walInfo); err != nil {
			return false, err
		}

		var deltaInfo lastDeltaInfo
		if err := lastBuildEntry.DecodeJSON(&deltaInfo); err != nil {
			return false, err
		}

		// Here, everything decoded properly and we know that no new certs
		// have been revoked since we built this last delta CRL. We can exit
		// without rebuilding then.
		if walInfo.Serial == deltaInfo.Serial {
			return false, nil
		}
	}

	return true, nil
}

func (cb *crlBuilder) rebuildDeltaCRLs(sc *storageContext, forceNew bool) error {
	cb._builder.Lock()
	defer cb._builder.Unlock()

	return cb.rebuildDeltaCRLsHoldingLock(sc, forceNew)
}

func (cb *crlBuilder) rebuildDeltaCRLsHoldingLock(sc *storageContext, forceNew bool) error {
	return buildAnyCRLs(sc, forceNew, true /* building delta */)
}

func (cb *crlBuilder) addCertForRevocationCheck(cluster, serial string) {
	entry := &revocationQueueEntry{
		Cluster: cluster,
		Serial:  serial,
	}
	cb.revQueue.Add(entry)
}

func (cb *crlBuilder) addCertForRevocationRemoval(cluster, serial string) {
	entry := &revocationQueueEntry{
		Cluster: cluster,
		Serial:  serial,
	}
	cb.removalQueue.Add(entry)
}

func (cb *crlBuilder) addCertFromCrossRevocation(cluster, serial string) {
	entry := &revocationQueueEntry{
		Cluster: cluster,
		Serial:  serial,
	}
	cb.crossQueue.Add(entry)
}

func (cb *crlBuilder) maybeGatherQueueForFirstProcess(sc *storageContext, isNotPerfPrimary bool) error {
	// Assume holding lock.
	if cb.haveInitializedQueue.Load() {
		return nil
	}

	sc.Backend.Logger().Debug(fmt.Sprintf("gathering first time existing revocations"))

	clusters, err := sc.Storage.List(sc.Context, crossRevocationPrefix)
	if err != nil {
		return fmt.Errorf("failed to list cross-cluster revocation queue participating clusters: %w", err)
	}

	sc.Backend.Logger().Debug(fmt.Sprintf("found %v clusters: %v", len(clusters), clusters))

	for cIndex, cluster := range clusters {
		cluster = cluster[0 : len(cluster)-1]
		cPath := crossRevocationPrefix + cluster + "/"
		serials, err := sc.Storage.List(sc.Context, cPath)
		if err != nil {
			return fmt.Errorf("failed to list cross-cluster revocation queue entries for cluster %v (%v): %w", cluster, cIndex, err)
		}

		sc.Backend.Logger().Debug(fmt.Sprintf("found %v serials for cluster %v: %v", len(serials), cluster, serials))

		for _, serial := range serials {
			if serial[len(serial)-1] == '/' {
				serial = serial[0 : len(serial)-1]
			}

			ePath := cPath + serial
			eConfirmPath := ePath + "/confirmed"
			removalEntry, err := sc.Storage.Get(sc.Context, eConfirmPath)

			entry := &revocationQueueEntry{
				Cluster: cluster,
				Serial:  serial,
			}

			// No removal entry yet; add to regular queue. Otherwise, slate it
			// for removal if we're a perfPrimary.
			if err != nil || removalEntry == nil {
				cb.revQueue.Add(entry)
			} else if !isNotPerfPrimary {
				cb.removalQueue.Add(entry)
			} // Else, this is a confirmation but we're on a perf secondary so ignore it.

			// Overwrite the error; we don't really care about its contents
			// at this step.
			err = nil
		}
	}

	return nil
}

func (cb *crlBuilder) processRevocationQueue(sc *storageContext) error {
	sc.Backend.Logger().Debug(fmt.Sprintf("starting to process revocation requests"))

	isNotPerfPrimary := sc.Backend.System().ReplicationState().HasState(consts.ReplicationDRSecondary|consts.ReplicationPerformanceStandby) ||
		(!sc.Backend.System().LocalMount() && sc.Backend.System().ReplicationState().HasState(consts.ReplicationPerformanceSecondary))

	if err := cb.maybeGatherQueueForFirstProcess(sc, isNotPerfPrimary); err != nil {
		return fmt.Errorf("failed to gather first queue: %v", err)
	}

	revQueue := cb.revQueue.Iterate()
	removalQueue := cb.removalQueue.Iterate()

	sc.Backend.Logger().Debug(fmt.Sprintf("gathered %v revocations and %v confirmation entries", len(revQueue), len(removalQueue)))

	crlConfig, err := cb.getConfigWithUpdate(sc)
	if err != nil {
		return err
	}

	ourClusterId, err := sc.Backend.System().ClusterID(sc.Context)
	if err != nil {
		return fmt.Errorf("unable to fetch clusterID to ignore local revocation entries: %w", err)
	}

	for _, req := range revQueue {
		// Regardless of whether we're on the perf primary or a secondary
		// cluster, we can safely ignore revocation requests originating
		// from our node, because we've already checked them once (when
		// they were created).
		if ourClusterId != "" && ourClusterId == req.Cluster {
			continue
		}

		// Fetch the revocation entry to ensure it exists.
		rPath := crossRevocationPrefix + req.Cluster + "/" + req.Serial
		entry, err := sc.Storage.Get(sc.Context, rPath)
		if err != nil {
			return fmt.Errorf("failed to read cross-cluster revocation queue entry: %w", err)
		}
		if entry == nil {
			// Skipping this entry; it was likely an incorrect invalidation
			// caused by the primary cluster removing the confirmation.
			cb.revQueue.Remove(req)
			continue
		}

		resp, err := tryRevokeCertBySerial(sc, crlConfig, req.Serial)
		if err == nil && resp != nil && !resp.IsError() && resp.Data != nil && resp.Data["state"].(string) == "revoked" {
			if isNotPerfPrimary {
				// Write a revocation queue removal entry.
				confirmed := revocationConfirmed{
					RevokedAt: resp.Data["revocation_time_rfc3339"].(string),
					Source:    req.Cluster,
				}
				path := crossRevocationPath + req.Serial + "/confirmed"
				confirmedEntry, err := logical.StorageEntryJSON(path, confirmed)
				if err != nil {
					return fmt.Errorf("failed to create storage entry for cross-cluster revocation confirmed response: %w", err)
				}

				if err := sc.Storage.Put(sc.Context, confirmedEntry); err != nil {
					return fmt.Errorf("error persisting cross-cluster revocation confirmation: %w\nThis may occur when the active node of the primary performance replication cluster is unavailable.", err)
				}
			} else {
				// Since we're the active node of the primary cluster, go ahead
				// and just remove it.
				path := crossRevocationPrefix + req.Cluster + "/" + req.Serial
				if err := sc.Storage.Delete(sc.Context, path); err != nil {
					return fmt.Errorf("failed to delete processed revocation request: %w", err)
				}
			}
		} else if err != nil {
			// Because we fake being from a lease, we get the guarantee that
			// err == nil == resp if the cert was already revoked; this means
			// this err should actually be fatal.
			return err
		}
		cb.revQueue.Remove(req)
	}

	if isNotPerfPrimary {
		sc.Backend.Logger().Debug(fmt.Sprintf("not on perf primary so ignoring any revocation confirmations"))

		// See note in pki/backend.go; this should be empty.
		cb.removalQueue.RemoveAll()
		cb.haveInitializedQueue.Store(true)
		return nil
	}

	clusters, err := sc.Storage.List(sc.Context, crossRevocationPrefix)
	if err != nil {
		return err
	}

	for _, entry := range removalQueue {
		// First remove the revocation request.
		for cIndex, cluster := range clusters {
			eEntry := crossRevocationPrefix + cluster + entry.Serial
			if err := sc.Storage.Delete(sc.Context, eEntry); err != nil {
				return fmt.Errorf("failed to delete potential cross-cluster revocation entry for cluster %v (%v) and serial %v: %w", cluster, cIndex, entry.Serial, err)
			}
		}

		// Then remove the confirmation.
		if err := sc.Storage.Delete(sc.Context, crossRevocationPrefix+entry.Cluster+"/"+entry.Serial+"/confirmed"); err != nil {
			return fmt.Errorf("failed to delete cross-cluster revocation confirmation entry for cluster %v and serial %v: %w", entry.Cluster, entry.Serial, err)
		}

		cb.removalQueue.Remove(entry)
	}

	cb.haveInitializedQueue.Store(true)

	return nil
}

func (cb *crlBuilder) processCrossClusterRevocations(sc *storageContext) error {
	sc.Backend.Logger().Debug(fmt.Sprintf("starting to process unified revocations"))

	crlConfig, err := cb.getConfigWithUpdate(sc)
	if err != nil {
		return err
	}

	if !crlConfig.UnifiedCRL {
		cb.crossQueue.RemoveAll()
		return nil
	}

	crossQueue := cb.crossQueue.Iterate()
	sc.Backend.Logger().Debug(fmt.Sprintf("gathered %v unified revocations entries", len(crossQueue)))

	ourClusterId, err := sc.Backend.System().ClusterID(sc.Context)
	if err != nil {
		return fmt.Errorf("unable to fetch clusterID to ignore local unified revocation entries: %w", err)
	}

	for _, req := range crossQueue {
		// Regardless of whether we're on the perf primary or a secondary
		// cluster, we can safely ignore revocation requests originating
		// from our node, because we've already checked them once (when
		// they were created).
		if ourClusterId != "" && ourClusterId == req.Cluster {
			continue
		}

		// Fetch the revocation entry to ensure it exists and this wasn't
		// a delete.
		rPath := unifiedRevocationReadPathPrefix + req.Cluster + "/" + req.Serial
		entry, err := sc.Storage.Get(sc.Context, rPath)
		if err != nil {
			return fmt.Errorf("failed to read unified revocation entry: %w", err)
		}
		if entry == nil {
			// Skip this entry: it was likely caused by the deletion of this
			// record during tidy.
			cb.crossQueue.Remove(req)
			continue
		}

		resp, err := tryRevokeCertBySerial(sc, crlConfig, req.Serial)
		if err == nil && resp != nil && !resp.IsError() && resp.Data != nil && resp.Data["state"].(string) == "revoked" {
			// We could theoretically save ourselves from writing a global
			// revocation entry during the above certificate revocation, as
			// we don't really need it to appear on either the unified CRL
			// or its delta CRL, but this would require more plumbing.
			cb.crossQueue.Remove(req)
		} else if err != nil {
			// Because we fake being from a lease, we get the guarantee that
			// err == nil == resp if the cert was already revoked; this means
			// this err should actually be fatal.
			return err
		}
	}

	return nil
}

// Helper function to fetch a map of issuerID->parsed cert for revocation
// usage. Unlike other paths, this needs to handle the legacy bundle
// more gracefully than rejecting it outright.
func fetchIssuerMapForRevocationChecking(sc *storageContext) (map[issuerID]*x509.Certificate, error) {
	var err error
	var issuers []issuerID

	if !sc.Backend.useLegacyBundleCaStorage() {
		issuers, err = sc.listIssuers()
		if err != nil {
			return nil, fmt.Errorf("could not fetch issuers list: %w", err)
		}
	} else {
		// Hack: this isn't a real issuerID, but it works for fetchCAInfo
		// since it resolves the reference.
		issuers = []issuerID{legacyBundleShimID}
	}

	issuerIDCertMap := make(map[issuerID]*x509.Certificate, len(issuers))
	for _, issuer := range issuers {
		_, bundle, caErr := sc.fetchCertBundleByIssuerId(issuer, false)
		if caErr != nil {
			return nil, fmt.Errorf("error fetching CA certificate for issuer id %v: %w", issuer, caErr)
		}

		if bundle == nil {
			return nil, fmt.Errorf("faulty reference: %v - CA info not found", issuer)
		}

		parsedBundle, err := parseCABundle(sc.Context, sc.Backend, bundle)
		if err != nil {
			return nil, errutil.InternalError{Err: err.Error()}
		}

		if parsedBundle.Certificate == nil {
			return nil, errutil.InternalError{Err: "stored CA information not able to be parsed"}
		}

		issuerIDCertMap[issuer] = parsedBundle.Certificate
	}

	return issuerIDCertMap, nil
}

// Revoke a certificate from a given serial number if it is present in local
// storage.
func tryRevokeCertBySerial(sc *storageContext, config *crlConfig, serial string) (*logical.Response, error) {
	// revokeCert requires us to hold these locks before calling it.
	sc.Backend.revokeStorageLock.Lock()
	defer sc.Backend.revokeStorageLock.Unlock()

	certEntry, err := fetchCertBySerial(sc, "certs/", serial)
	if err != nil {
		switch err.(type) {
		case errutil.UserError:
			return logical.ErrorResponse(err.Error()), nil
		default:
			return nil, err
		}
	}

	if certEntry == nil {
		return nil, nil
	}

	cert, err := x509.ParseCertificate(certEntry.Value)
	if err != nil {
		return nil, fmt.Errorf("error parsing certificate: %w", err)
	}

	return revokeCert(sc, config, cert)
}

// Revokes a cert, and tries to be smart about error recovery
func revokeCert(sc *storageContext, config *crlConfig, cert *x509.Certificate) (*logical.Response, error) {
	// As this backend is self-contained and this function does not hook into
	// third parties to manage users or resources, if the mount is tainted,
	// revocation doesn't matter anyways -- the CRL that would be written will
	// be immediately blown away by the view being cleared. So we can simply
	// fast path a successful exit.
	if sc.Backend.System().Tainted() {
		return nil, nil
	}

	colonSerial := serialFromCert(cert)
	hyphenSerial := normalizeSerial(colonSerial)

	// Validate that no issuers match the serial number to be revoked. We need
	// to gracefully degrade to the legacy cert bundle when it is required, as
	// secondary PR clusters might not have been upgraded, but still need to
	// handle revoking certs.
	issuerIDCertMap, err := fetchIssuerMapForRevocationChecking(sc)
	if err != nil {
		return nil, err
	}

	// Ensure we don't revoke an issuer via this API; use /issuer/:issuer_ref/revoke
	// instead.
	for issuer, certificate := range issuerIDCertMap {
		if colonSerial == serialFromCert(certificate) {
			return logical.ErrorResponse(fmt.Sprintf("adding issuer (id: %v) to its own CRL is not allowed", issuer)), nil
		}
	}

	curRevInfo, err := sc.fetchRevocationInfo(colonSerial)
	if err != nil {
		return nil, err
	}
	if curRevInfo != nil {
		resp := &logical.Response{
			Data: map[string]interface{}{
				"revocation_time": curRevInfo.RevocationTime,
				"state":           "revoked",
			},
		}
		if !curRevInfo.RevocationTimeUTC.IsZero() {
			resp.Data["revocation_time_rfc3339"] = curRevInfo.RevocationTimeUTC.Format(time.RFC3339Nano)
		}

		return resp, nil
	}

	// Add a little wiggle room because leases are stored with a second
	// granularity
	if cert.NotAfter.Before(time.Now().Add(2 * time.Second)) {
		response := &logical.Response{}
		response.AddWarning(fmt.Sprintf("certificate with serial %s already expired; refusing to add to CRL", colonSerial))
		return response, nil
	}

	currTime := time.Now()
	revInfo := revocationInfo{
		CertificateBytes:  cert.Raw,
		RevocationTime:    currTime.Unix(),
		RevocationTimeUTC: currTime.UTC(),
	}

	// We may not find an issuer with this certificate; that's fine so
	// ignore the return value.
	associateRevokedCertWithIsssuer(&revInfo, cert, issuerIDCertMap)

	revEntry, err := logical.StorageEntryJSON(revokedPath+hyphenSerial, revInfo)
	if err != nil {
		return nil, fmt.Errorf("error creating revocation entry")
	}

	certsCounted := sc.Backend.certsCounted.Load()
	err = sc.Storage.Put(sc.Context, revEntry)
	if err != nil {
		return nil, fmt.Errorf("error saving revoked certificate to new location")
	}
	sc.Backend.incrementTotalRevokedCertificatesCount(certsCounted, revEntry.Key)

	// If this flag is enabled after the fact, existing local entries will be published to
	// the unified storage space through a periodic function.
	if config.UnifiedCRL {
		entry := &unifiedRevocationEntry{
			SerialNumber:      colonSerial,
			CertExpiration:    cert.NotAfter,
			RevocationTimeUTC: revInfo.RevocationTimeUTC,
			CertificateIssuer: revInfo.CertificateIssuer,
		}

		ignoreErr := writeUnifiedRevocationEntry(sc, entry)
		if ignoreErr != nil {
			// Just log the error if we fail to write across clusters, a separate background
			// thread will reattempt it later on as we have the local write done.
			sc.Backend.Logger().Debug("Failed to write unified revocation entry, will re-attempt later",
				"serial_number", colonSerial, "error", ignoreErr)
			sc.Backend.unifiedTransferStatus.forceRun()
		}
	}

	if !config.AutoRebuild {
		// Note that writing the Delta WAL here isn't necessary; we've
		// already rebuilt the full CRL so the Delta WAL will be cleared
		// afterwards. Writing an entry only to immediately remove it
		// isn't necessary.
		crlErr := sc.Backend.crlBuilder.rebuild(sc, false)
		if crlErr != nil {
			switch crlErr.(type) {
			case errutil.UserError:
				return logical.ErrorResponse(fmt.Sprintf("Error during CRL building: %s", crlErr)), nil
			default:
				return nil, fmt.Errorf("error encountered during CRL building: %w", crlErr)
			}
		}
	} else if config.EnableDelta {
		if err := writeRevocationDeltaWALs(sc, config, hyphenSerial, colonSerial); err != nil {
			return nil, fmt.Errorf("failed to write WAL entries for Delta CRLs: %w", err)
		}
	}

	return &logical.Response{
		Data: map[string]interface{}{
			"revocation_time":         revInfo.RevocationTime,
			"revocation_time_rfc3339": revInfo.RevocationTimeUTC.Format(time.RFC3339Nano),
			"state":                   "revoked",
		},
	}, nil
}

func writeRevocationDeltaWALs(sc *storageContext, config *crlConfig, hyphenSerial string, colonSerial string) error {
	if err := writeSpecificRevocationDeltaWALs(sc, hyphenSerial, colonSerial, localDeltaWALPath); err != nil {
		return fmt.Errorf("failed to write local delta WAL entry: %w", err)
	}

	if config.UnifiedCRL {
		// We only need to write cross-cluster unified Delta WAL entries when
		// it is enabled; in particular, because we rebuild CRLs when enabling
		// this flag, any revocations that happened prior to enabling unified
		// revocation will appear on the complete CRL (+/- synchronization:
		// in particular, if a perf replica revokes a cert prior to seeing
		// unified revocation enabled, but after the main node has done the
		// listing for the unified CRL rebuild, this revocation will not
		// appear on either the main or the next delta CRL, but will need to
		// wait for a subsequent complete CRL rebuild).
		if err := writeSpecificRevocationDeltaWALs(sc, hyphenSerial, colonSerial, unifiedDeltaWALPath); err != nil {
			return fmt.Errorf("failed to write cross-cluster delta WAL entry: %w", err)
		}
	}

	return nil
}

func writeSpecificRevocationDeltaWALs(sc *storageContext, hyphenSerial string, colonSerial string, pathPrefix string) error {
	// Previously, regardless of whether or not we've presently enabled
	// Delta CRLs, we would always write the Delta WAL in case it is
	// enabled in the future. We though we could trigger another full CRL
	// rebuild instead (to avoid inconsistent state between the CRL and
	// missing Delta WAL entries), but writing extra (unused?) WAL entries
	// versus an expensive full CRL rebuild was thought of as being
	// probably a net wash.
	//
	// However, we've now added unified CRL building, adding cross-cluster
	// writes to the revocation path. Because this is relatively expensive,
	// we've opted to rebuild the complete+delta CRLs when toggling the
	// state of delta enabled, instead of always writing delta CRL entries.
	//
	// Thus Delta WAL building happens **only** when Delta CRLs are enabled.
	//
	// We should only do this when the cert hasn't already been revoked.
	// Otherwise, the re-revocation may appear on both an existing CRL and
	// on a delta CRL, or a serial may be skipped from the delta CRL if
	// there's an A->B->A revocation pattern and the delta was rebuilt
	// after the first cert.
	//
	// Currently we don't store any data in the WAL entry.
	var walInfo deltaWALInfo
	walEntry, err := logical.StorageEntryJSON(pathPrefix+hyphenSerial, walInfo)
	if err != nil {
		return fmt.Errorf("unable to create delta CRL WAL entry")
	}

	if err = sc.Storage.Put(sc.Context, walEntry); err != nil {
		return fmt.Errorf("error saving delta CRL WAL entry")
	}

	// In order for periodic delta rebuild to be mildly efficient, we
	// should write the last revoked delta WAL entry so we know if we
	// have new revocations that we should rebuild the delta WAL for.
	lastRevSerial := lastWALInfo{Serial: colonSerial}
	lastWALEntry, err := logical.StorageEntryJSON(pathPrefix+deltaWALLastRevokedSerialName, lastRevSerial)
	if err != nil {
		return fmt.Errorf("unable to create last delta CRL WAL entry")
	}
	if err = sc.Storage.Put(sc.Context, lastWALEntry); err != nil {
		return fmt.Errorf("error saving last delta CRL WAL entry")
	}

	return nil
}

func buildCRLs(sc *storageContext, forceNew bool) error {
	return buildAnyCRLs(sc, forceNew, false)
}

func buildAnyCRLs(sc *storageContext, forceNew bool, isDelta bool) error {
	// In order to build all CRLs, we need knowledge of all issuers. Any two
	// issuers with the same keys _and_ subject should have the same CRL since
	// they're functionally equivalent.
	//
	// When building CRLs, there's two types of CRLs: an "internal" CRL for
	// just certificates issued by this issuer, and a "default" CRL, which
	// not only contains certificates by this issuer, but also ones issued
	// by "unknown" or past issuers. This means we need knowledge of not
	// only all issuers (to tell whether or not to include these orphaned
	// certs) but whether the present issuer is the configured default.
	//
	// If a configured default is lacking, we won't provision these
	// certificates on any CRL.
	//
	// In order to know which CRL a given cert belongs on, we have to read
	// it into memory, identify the corresponding issuer, and update its
	// map with the revoked cert instance. If no such issuer is found, we'll
	// place it in the default issuer's CRL.
	//
	// By not relying on the _cert_'s storage, we allow issuers to come and
	// go (either by direct deletion, having their keys deleted, or by usage
	// restrictions) -- and when they return, we'll correctly place certs
	// on their CRLs.

	// See the message in revokedCert about rebuilding CRLs: we need to
	// gracefully handle revoking entries with the legacy cert bundle.
	var err error
	var issuers []issuerID
	var wasLegacy bool

	// First, fetch an updated copy of the CRL config. We'll pass this into
	// buildCRL.
	globalCRLConfig, err := sc.Backend.crlBuilder.getConfigWithUpdate(sc)
	if err != nil {
		return fmt.Errorf("error building CRL: while updating config: %w", err)
	}

	if globalCRLConfig.Disable && !forceNew {
		// We build a single long-lived (but regular validity) empty CRL in
		// the event that we disable the CRL, but we don't keep updating it
		// with newer, more-valid empty CRLs in the event that we later
		// re-enable it. This is a historical behavior.
		//
		// So, since tidy can now associate issuers on revocation entries, we
		// can skip the rest of this function and exit early without updating
		// anything.
		return nil
	}

	if !sc.Backend.useLegacyBundleCaStorage() {
		issuers, err = sc.listIssuers()
		if err != nil {
			return fmt.Errorf("error building CRL: while listing issuers: %w", err)
		}
	} else {
		// Here, we hard-code the legacy issuer entry instead of using the
		// default ref. This is because we need to hack some of the logic
		// below for revocation to handle the legacy bundle.
		issuers = []issuerID{legacyBundleShimID}
		wasLegacy = true

		// Here, we avoid building a delta CRL with the legacy CRL bundle.
		//
		// Users should upgrade symmetrically, rather than attempting
		// backward compatibility for new features across disparate versions.
		if isDelta {
			return nil
		}
	}

	issuersConfig, err := sc.getIssuersConfig()
	if err != nil {
		return fmt.Errorf("error building CRLs: while getting the default config: %w", err)
	}

	// We map issuerID->entry for fast lookup and also issuerID->Cert for
	// signature verification and correlation of revoked certs.
	issuerIDEntryMap := make(map[issuerID]*issuerEntry, len(issuers))
	issuerIDCertMap := make(map[issuerID]*x509.Certificate, len(issuers))

	// We use a double map (keyID->subject->issuerID) to store whether or not this
	// key+subject paring has been seen before. We can then iterate over each
	// key/subject and choose any representative issuer for that combination.
	keySubjectIssuersMap := make(map[keyID]map[string][]issuerID)
	for _, issuer := range issuers {
		// We don't strictly need this call, but by requesting the bundle, the
		// legacy path is automatically ignored.
		thisEntry, _, err := sc.fetchCertBundleByIssuerId(issuer, false)
		if err != nil {
			return fmt.Errorf("error building CRLs: unable to fetch specified issuer (%v): %w", issuer, err)
		}

		if len(thisEntry.KeyID) == 0 {
			continue
		}

		// n.b.: issuer usage check has been delayed. This occurred because
		// we want to ensure any issuer (representative of a larger set) can
		// be used to associate revocation entries and we won't bother
		// rewriting that entry (causing churn) if the particular selected
		// issuer lacks CRL signing capabilities.
		//
		// The result is that this map (and the other maps) contain all the
		// issuers we know about, and only later do we check crlSigning before
		// choosing our representative.
		//
		// The other side effect (making this not compatible with Vault 1.11
		// behavior) is that _identified_ certificates whose issuer set is
		// not allowed for crlSigning will no longer appear on the default
		// issuer's CRL.
		issuerIDEntryMap[issuer] = thisEntry

		thisCert, err := thisEntry.GetCertificate()
		if err != nil {
			return fmt.Errorf("error building CRLs: unable to parse issuer (%v)'s certificate: %w", issuer, err)
		}
		issuerIDCertMap[issuer] = thisCert

		subject := string(thisCert.RawSubject)
		if _, ok := keySubjectIssuersMap[thisEntry.KeyID]; !ok {
			keySubjectIssuersMap[thisEntry.KeyID] = make(map[string][]issuerID)
		}

		keySubjectIssuersMap[thisEntry.KeyID][subject] = append(keySubjectIssuersMap[thisEntry.KeyID][subject], issuer)
	}

	// Now we do two calls: building the cluster-local CRL, and potentially
	// building the global CRL if we're on the active node of the performance
	// primary.
	currLocalDeltaSerials, err := buildAnyLocalCRLs(sc, issuersConfig, globalCRLConfig,
		issuers, issuerIDEntryMap,
		issuerIDCertMap, keySubjectIssuersMap,
		wasLegacy, forceNew, isDelta)
	if err != nil {
		return err
	}
	currUnifiedDeltaSerials, err := buildAnyUnifiedCRLs(sc, issuersConfig, globalCRLConfig,
		issuers, issuerIDEntryMap,
		issuerIDCertMap, keySubjectIssuersMap,
		wasLegacy, forceNew, isDelta)
	if err != nil {
		return err
	}

	// Finally, we decide if we need to rebuild the Delta CRLs again, for both
	// global and local CRLs if necessary.
	if !isDelta {
		// After we've confirmed the primary CRLs have built OK, go ahead and
		// clear the delta CRL WAL and rebuild it.
		if err := sc.Backend.crlBuilder.clearLocalDeltaWAL(sc, currLocalDeltaSerials); err != nil {
			return fmt.Errorf("error building CRLs: unable to clear Delta WAL: %w", err)
		}
		if err := sc.Backend.crlBuilder.clearUnifiedDeltaWAL(sc, currUnifiedDeltaSerials); err != nil {
			return fmt.Errorf("error building CRLs: unable to clear Delta WAL: %w", err)
		}
		if err := sc.Backend.crlBuilder.rebuildDeltaCRLsHoldingLock(sc, forceNew); err != nil {
			return fmt.Errorf("error building CRLs: unable to rebuild empty Delta WAL: %w", err)
		}
	}

	return nil
}

func getLastWALSerial(sc *storageContext, path string) (string, error) {
	lastWALEntry, err := sc.Storage.Get(sc.Context, localDeltaWALLastRevokedSerial)
	if err != nil {
		return "", err
	}

	if lastWALEntry != nil && lastWALEntry.Value != nil {
		var walInfo lastWALInfo
		if err := lastWALEntry.DecodeJSON(&walInfo); err != nil {
			return "", err
		}

		return walInfo.Serial, nil
	}

	// No serial to return.
	return "", nil
}

func buildAnyLocalCRLs(
	sc *storageContext,
	issuersConfig *issuerConfigEntry,
	globalCRLConfig *crlConfig,
	issuers []issuerID,
	issuerIDEntryMap map[issuerID]*issuerEntry,
	issuerIDCertMap map[issuerID]*x509.Certificate,
	keySubjectIssuersMap map[keyID]map[string][]issuerID,
	wasLegacy bool,
	forceNew bool,
	isDelta bool,
) ([]string, error) {
	var err error

	// Before we load cert entries, we want to store the last seen delta WAL
	// serial number. The subsequent List will have at LEAST that certificate
	// (and potentially more) in it; when we're done writing the delta CRL,
	// we'll write this serial as a sentinel to see if we need to rebuild it
	// in the future.
	var lastDeltaSerial string
	if isDelta {
		lastDeltaSerial, err = getLastWALSerial(sc, localDeltaWALLastRevokedSerial)
		if err != nil {
			return nil, err
		}
	}

	// We fetch a list of delta WAL entries prior to generating the complete
	// CRL. This allows us to avoid a lock (to clear such storage): anything
	// visible now, should also be visible on the complete CRL we're writing.
	var currDeltaCerts []string
	if !isDelta {
		currDeltaCerts, err = sc.Backend.crlBuilder.getPresentLocalDeltaWALForClearing(sc)
		if err != nil {
			return nil, fmt.Errorf("error building CRLs: unable to get present delta WAL entries for removal: %w", err)
		}
	}

	var unassignedCerts []pkix.RevokedCertificate
	var revokedCertsMap map[issuerID][]pkix.RevokedCertificate

	// If the CRL is disabled do not bother reading in all the revoked certificates.
	if !globalCRLConfig.Disable {
		// Next, we load and parse all revoked certificates. We need to assign
		// these certificates to an issuer. Some certificates will not be
		// assignable (if they were issued by a since-deleted issuer), so we need
		// a separate pool for those.
		unassignedCerts, revokedCertsMap, err = getLocalRevokedCertEntries(sc, issuerIDCertMap, isDelta)
		if err != nil {
			return nil, fmt.Errorf("error building CRLs: unable to get revoked certificate entries: %w", err)
		}

		if !isDelta {
			// Revoking an issuer forces us to rebuild our complete CRL,
			// regardless of whether or not we've enabled auto rebuilding or
			// delta CRLs. If we elide the above isDelta check, this results
			// in a non-empty delta CRL, containing the serial of the
			// now-revoked issuer, even though it was generated _after_ the
			// complete CRL with the issuer on it. There's no reason to
			// duplicate this serial number on the delta, hence the above
			// guard for isDelta.
			if err := augmentWithRevokedIssuers(issuerIDEntryMap, issuerIDCertMap, revokedCertsMap); err != nil {
				return nil, fmt.Errorf("error building CRLs: unable to parse revoked issuers: %w", err)
			}
		}
	}

	// Fetch the cluster-local CRL mapping so we know where to write the
	// CRLs.
	internalCRLConfig, err := sc.getLocalCRLConfig()
	if err != nil {
		return nil, fmt.Errorf("error building CRLs: unable to fetch cluster-local CRL configuration: %w", err)
	}

	if err := buildAnyCRLsWithCerts(sc, issuersConfig, globalCRLConfig, internalCRLConfig,
		issuers, issuerIDEntryMap, keySubjectIssuersMap,
		unassignedCerts, revokedCertsMap,
		forceNew, false /* isUnified */, isDelta); err != nil {
		return nil, fmt.Errorf("error building CRLs: %w", err)
	}

	// Finally, persist our potentially updated local CRL config. Only do this
	// if we didn't have a legacy CRL bundle.
	if !wasLegacy {
		if err := sc.setLocalCRLConfig(internalCRLConfig); err != nil {
			return nil, fmt.Errorf("error building CRLs: unable to persist updated cluster-local CRL config: %w", err)
		}
	}

	if isDelta {
		// Update our last build time here so we avoid checking for new certs
		// for a while.
		sc.Backend.crlBuilder.lastDeltaRebuildCheck = time.Now()

		if len(lastDeltaSerial) > 0 {
			// When we have a last delta serial, write out the relevant info
			// so we can skip extra CRL rebuilds.
			deltaInfo := lastDeltaInfo{Serial: lastDeltaSerial}

			lastDeltaBuildEntry, err := logical.StorageEntryJSON(localDeltaWALLastBuildSerial, deltaInfo)
			if err != nil {
				return nil, fmt.Errorf("error creating last delta CRL rebuild serial entry: %w", err)
			}

			err = sc.Storage.Put(sc.Context, lastDeltaBuildEntry)
			if err != nil {
				return nil, fmt.Errorf("error persisting last delta CRL rebuild info: %w", err)
			}
		}
	}

	return currDeltaCerts, nil
}

func buildAnyUnifiedCRLs(
	sc *storageContext,
	issuersConfig *issuerConfigEntry,
	globalCRLConfig *crlConfig,
	issuers []issuerID,
	issuerIDEntryMap map[issuerID]*issuerEntry,
	issuerIDCertMap map[issuerID]*x509.Certificate,
	keySubjectIssuersMap map[keyID]map[string][]issuerID,
	wasLegacy bool,
	forceNew bool,
	isDelta bool,
) ([]string, error) {
	var err error

	// Unified CRL can only be built by the main cluster.
	b := sc.Backend
	if b.System().ReplicationState().HasState(consts.ReplicationDRSecondary|consts.ReplicationPerformanceStandby) ||
		(!b.System().LocalMount() && b.System().ReplicationState().HasState(consts.ReplicationPerformanceSecondary)) {
		return nil, nil
	}

	// Unified CRL should only be built if enabled.
	if !globalCRLConfig.UnifiedCRL && !forceNew {
		return nil, nil
	}

	// Before we load cert entries, we want to store the last seen delta WAL
	// serial number. The subsequent List will have at LEAST that certificate
	// (and potentially more) in it; when we're done writing the delta CRL,
	// we'll write this serial as a sentinel to see if we need to rebuild it
	// in the future.
	var lastDeltaSerial string
	if isDelta {
		lastDeltaSerial, err = getLastWALSerial(sc, unifiedDeltaWALLastRevokedSerial)
		if err != nil {
			return nil, err
		}
	}

	// We fetch a list of delta WAL entries prior to generating the complete
	// CRL. This allows us to avoid a lock (to clear such storage): anything
	// visible now, should also be visible on the complete CRL we're writing.
	var currDeltaCerts []string
	if !isDelta {
		currDeltaCerts, err = sc.Backend.crlBuilder.getPresentUnifiedDeltaWALForClearing(sc)
		if err != nil {
			return nil, fmt.Errorf("error building CRLs: unable to get present delta WAL entries for removal: %w", err)
		}
	}

	var unassignedCerts []pkix.RevokedCertificate
	var revokedCertsMap map[issuerID][]pkix.RevokedCertificate

	// If the CRL is disabled do not bother reading in all the revoked certificates.
	if !globalCRLConfig.Disable {
		// Next, we load and parse all revoked certificates. We need to assign
		// these certificates to an issuer. Some certificates will not be
		// assignable (if they were issued by a since-deleted issuer), so we need
		// a separate pool for those.
		unassignedCerts, revokedCertsMap, err = getUnifiedRevokedCertEntries(sc, issuerIDCertMap, isDelta)
		if err != nil {
			return nil, fmt.Errorf("error building CRLs: unable to get revoked certificate entries: %w", err)
		}

		if !isDelta {
			// Revoking an issuer forces us to rebuild our complete CRL,
			// regardless of whether or not we've enabled auto rebuilding or
			// delta CRLs. If we elide the above isDelta check, this results
			// in a non-empty delta CRL, containing the serial of the
			// now-revoked issuer, even though it was generated _after_ the
			// complete CRL with the issuer on it. There's no reason to
			// duplicate this serial number on the delta, hence the above
			// guard for isDelta.
			if err := augmentWithRevokedIssuers(issuerIDEntryMap, issuerIDCertMap, revokedCertsMap); err != nil {
				return nil, fmt.Errorf("error building CRLs: unable to parse revoked issuers: %w", err)
			}
		}
	}

	// Fetch the cluster-local CRL mapping so we know where to write the
	// CRLs.
	internalCRLConfig, err := sc.getUnifiedCRLConfig()
	if err != nil {
		return nil, fmt.Errorf("error building CRLs: unable to fetch cluster-local CRL configuration: %w", err)
	}

	if err := buildAnyCRLsWithCerts(sc, issuersConfig, globalCRLConfig, internalCRLConfig,
		issuers, issuerIDEntryMap, keySubjectIssuersMap,
		unassignedCerts, revokedCertsMap,
		forceNew, true /* isUnified */, isDelta); err != nil {
		return nil, fmt.Errorf("error building CRLs: %w", err)
	}

	// Finally, persist our potentially updated local CRL config. Only do this
	// if we didn't have a legacy CRL bundle.
	if !wasLegacy {
		if err := sc.setUnifiedCRLConfig(internalCRLConfig); err != nil {
			return nil, fmt.Errorf("error building CRLs: unable to persist updated cluster-local CRL config: %w", err)
		}
	}

	if isDelta {
		// Update our last build time here so we avoid checking for new certs
		// for a while.
		sc.Backend.crlBuilder.lastDeltaRebuildCheck = time.Now()

		if len(lastDeltaSerial) > 0 {
			// When we have a last delta serial, write out the relevant info
			// so we can skip extra CRL rebuilds.
			deltaInfo := lastDeltaInfo{Serial: lastDeltaSerial}

			lastDeltaBuildEntry, err := logical.StorageEntryJSON(unifiedDeltaWALLastBuildSerial, deltaInfo)
			if err != nil {
				return nil, fmt.Errorf("error creating last delta CRL rebuild serial entry: %w", err)
			}

			err = sc.Storage.Put(sc.Context, lastDeltaBuildEntry)
			if err != nil {
				return nil, fmt.Errorf("error persisting last delta CRL rebuild info: %w", err)
			}
		}
	}

	return currDeltaCerts, nil
}

func buildAnyCRLsWithCerts(
	sc *storageContext,
	issuersConfig *issuerConfigEntry,
	globalCRLConfig *crlConfig,
	internalCRLConfig *internalCRLConfigEntry,
	issuers []issuerID,
	issuerIDEntryMap map[issuerID]*issuerEntry,
	keySubjectIssuersMap map[keyID]map[string][]issuerID,
	unassignedCerts []pkix.RevokedCertificate,
	revokedCertsMap map[issuerID][]pkix.RevokedCertificate,
	forceNew bool,
	isUnified bool,
	isDelta bool,
) error {
	// Now we can call buildCRL once, on an arbitrary/representative issuer
	// from each of these (keyID, subject) sets.
	for _, subjectIssuersMap := range keySubjectIssuersMap {
		for _, issuersSet := range subjectIssuersMap {
			if len(issuersSet) == 0 {
				continue
			}

			var revokedCerts []pkix.RevokedCertificate
			representative := issuerID("")
			var crlIdentifier crlID
			var crlIdIssuer issuerID
			for _, issuerId := range issuersSet {
				// Skip entries which aren't enabled for CRL signing. We don't
				// particularly care which issuer is ultimately chosen as the
				// set representative for signing at this point, other than
				// that it has crl-signing usage.
				if err := issuerIDEntryMap[issuerId].EnsureUsage(CRLSigningUsage); err != nil {
					continue
				}

				// Prefer to use the default as the representative of this
				// set, if it is a member.
				//
				// If it is, we'll also pull in the unassigned certs to remain
				// compatible with Vault's earlier, potentially questionable
				// behavior.
				if issuerId == issuersConfig.DefaultIssuerId {
					if len(unassignedCerts) > 0 {
						revokedCerts = append(revokedCerts, unassignedCerts...)
					}

					representative = issuerId
				}

				// Otherwise, use any other random issuer if we've not yet
				// chosen one.
				if representative == issuerID("") {
					representative = issuerId
				}

				// Pull in the revoked certs associated with this member.
				if thisRevoked, ok := revokedCertsMap[issuerId]; ok && len(thisRevoked) > 0 {
					revokedCerts = append(revokedCerts, thisRevoked...)
				}

				// Finally, check our crlIdentifier.
				if thisCRLId, ok := internalCRLConfig.IssuerIDCRLMap[issuerId]; ok && len(thisCRLId) > 0 {
					if len(crlIdentifier) > 0 && crlIdentifier != thisCRLId {
						return fmt.Errorf("error building CRLs: two issuers with same keys/subjects (%v vs %v) have different internal CRL IDs: %v vs %v", issuerId, crlIdIssuer, thisCRLId, crlIdentifier)
					}

					crlIdentifier = thisCRLId
					crlIdIssuer = issuerId
				}
			}

			if representative == "" {
				// Skip this set for the time being; while we have valid
				// issuers and associated keys, this occurred because we lack
				// crl-signing usage on all issuers in this set.
				continue
			}

			if len(crlIdentifier) == 0 {
				// Create a new random UUID for this CRL if none exists.
				crlIdentifier = genCRLId()
				internalCRLConfig.CRLNumberMap[crlIdentifier] = 1
			}

			// Update all issuers in this group to set the CRL Issuer
			for _, issuerId := range issuersSet {
				internalCRLConfig.IssuerIDCRLMap[issuerId] = crlIdentifier
			}

			// We always update the CRL Number since we never want to
			// duplicate numbers and missing numbers is fine.
			crlNumber := internalCRLConfig.CRLNumberMap[crlIdentifier]
			internalCRLConfig.CRLNumberMap[crlIdentifier] += 1

			// CRLs (regardless of complete vs delta) are incrementally
			// numbered. But delta CRLs need to know the number of the
			// last complete CRL. We assume that's the previous identifier
			// if no value presently exists.
			lastCompleteNumber, haveLast := internalCRLConfig.LastCompleteNumberMap[crlIdentifier]
			if !haveLast {
				// We use the value of crlNumber for the current CRL, so
				// decrement it by one to find the last one.
				lastCompleteNumber = crlNumber - 1
			}

			// Update `LastModified`
			if isDelta {
				internalCRLConfig.DeltaLastModified = time.Now().UTC()
			} else {
				internalCRLConfig.LastModified = time.Now().UTC()
			}

			// Lastly, build the CRL.
			nextUpdate, err := buildCRL(sc, globalCRLConfig, forceNew, representative, revokedCerts, crlIdentifier, crlNumber, isUnified, isDelta, lastCompleteNumber)
			if err != nil {
				return fmt.Errorf("error building CRLs: unable to build CRL for issuer (%v): %w", representative, err)
			}

			internalCRLConfig.CRLExpirationMap[crlIdentifier] = *nextUpdate
			if !isDelta {
				internalCRLConfig.LastCompleteNumberMap[crlIdentifier] = crlNumber
			} else if !haveLast {
				// Since we're writing this config anyways, save our guess
				// as to the last CRL number.
				internalCRLConfig.LastCompleteNumberMap[crlIdentifier] = lastCompleteNumber
			}
		}
	}

	// Before persisting our updated CRL config, check to see if we have
	// any dangling references. If we have any issuers that don't exist,
	// remove them, remembering their CRLs IDs. If we've completely removed
	// all issuers pointing to that CRL number, we can remove it from the
	// number map and from storage.
	//
	// Note that we persist the last generated CRL for a specified issuer
	// if it is later disabled for CRL generation. This mirrors the old
	// root deletion behavior, but using soft issuer deletes. If there is an
	// alternate, equivalent issuer however, we'll keep updating the shared
	// CRL; all equivalent issuers must have their CRLs disabled.
	for mapIssuerId := range internalCRLConfig.IssuerIDCRLMap {
		stillHaveIssuer := false
		for _, listedIssuerId := range issuers {
			if mapIssuerId == listedIssuerId {
				stillHaveIssuer = true
				break
			}
		}

		if !stillHaveIssuer {
			delete(internalCRLConfig.IssuerIDCRLMap, mapIssuerId)
		}
	}
	for crlId := range internalCRLConfig.CRLNumberMap {
		stillHaveIssuerForID := false
		for _, remainingCRL := range internalCRLConfig.IssuerIDCRLMap {
			if remainingCRL == crlId {
				stillHaveIssuerForID = true
				break
			}
		}

		if !stillHaveIssuerForID {
			if err := sc.Storage.Delete(sc.Context, "crls/"+crlId.String()); err != nil {
				return fmt.Errorf("error building CRLs: unable to clean up deleted issuers' CRL: %w", err)
			}
		}
	}

	// All good :-)
	return nil
}

func isRevInfoIssuerValid(revInfo *revocationInfo, issuerIDCertMap map[issuerID]*x509.Certificate) bool {
	if len(revInfo.CertificateIssuer) > 0 {
		issuerId := revInfo.CertificateIssuer
		if _, issuerExists := issuerIDCertMap[issuerId]; issuerExists {
			return true
		}
	}

	return false
}

func associateRevokedCertWithIsssuer(revInfo *revocationInfo, revokedCert *x509.Certificate, issuerIDCertMap map[issuerID]*x509.Certificate) bool {
	for issuerId, issuerCert := range issuerIDCertMap {
		if bytes.Equal(revokedCert.RawIssuer, issuerCert.RawSubject) {
			if err := revokedCert.CheckSignatureFrom(issuerCert); err == nil {
				// Valid mapping. Add it to the specified entry.
				revInfo.CertificateIssuer = issuerId
				return true
			}
		}
	}

	return false
}

func getLocalRevokedCertEntries(sc *storageContext, issuerIDCertMap map[issuerID]*x509.Certificate, isDelta bool) ([]pkix.RevokedCertificate, map[issuerID][]pkix.RevokedCertificate, error) {
	var unassignedCerts []pkix.RevokedCertificate
	revokedCertsMap := make(map[issuerID][]pkix.RevokedCertificate)

	listingPath := revokedPath
	if isDelta {
		listingPath = localDeltaWALPath
	}

	revokedSerials, err := sc.Storage.List(sc.Context, listingPath)
	if err != nil {
		return nil, nil, errutil.InternalError{Err: fmt.Sprintf("error fetching list of revoked certs: %s", err)}
	}

	// Build a mapping of issuer serial -> certificate.
	issuerSerialCertMap := make(map[string][]*x509.Certificate, len(issuerIDCertMap))
	for _, cert := range issuerIDCertMap {
		serialStr := serialFromCert(cert)
		issuerSerialCertMap[serialStr] = append(issuerSerialCertMap[serialStr], cert)
	}

	for _, serial := range revokedSerials {
		if isDelta && (serial == deltaWALLastBuildSerialName || serial == deltaWALLastRevokedSerialName) {
			// Skip our placeholder entries...
			continue
		}

		var revInfo revocationInfo
		revokedEntry, err := sc.Storage.Get(sc.Context, revokedPath+serial)
		if err != nil {
			return nil, nil, errutil.InternalError{Err: fmt.Sprintf("unable to fetch revoked cert with serial %s: %s", serial, err)}
		}

		if revokedEntry == nil {
			return nil, nil, errutil.InternalError{Err: fmt.Sprintf("revoked certificate entry for serial %s is nil", serial)}
		}
		if revokedEntry.Value == nil || len(revokedEntry.Value) == 0 {
			// TODO: In this case, remove it and continue? How likely is this to
			// happen? Alternately, could skip it entirely, or could implement a
			// delete function so that there is a way to remove these
			return nil, nil, errutil.InternalError{Err: "found revoked serial but actual certificate is empty"}
		}

		err = revokedEntry.DecodeJSON(&revInfo)
		if err != nil {
			return nil, nil, errutil.InternalError{Err: fmt.Sprintf("error decoding revocation entry for serial %s: %s", serial, err)}
		}

		revokedCert, err := x509.ParseCertificate(revInfo.CertificateBytes)
		if err != nil {
			return nil, nil, errutil.InternalError{Err: fmt.Sprintf("unable to parse stored revoked certificate with serial %s: %s", serial, err)}
		}

		// We want to skip issuer certificate's revocationEntries for two
		// reasons:
		//
		// 1. We canonically use augmentWithRevokedIssuers to handle this
		//    case and this entry is just a backup. This prevents the issue
		//    of duplicate serial numbers on the CRL from both paths.
		// 2. We want to avoid a root's serial from appearing on its own
		//    CRL. If it is a cross-signed or re-issued variant, this is OK,
		//    but in the case we mark the root itself as "revoked", we want
		//    to avoid it appearing on the CRL as that is definitely
		//    undefined/little-supported behavior.
		//
		// This hash map lookup should be faster than byte comparison against
		// each issuer proactively.
		if candidates, present := issuerSerialCertMap[serialFromCert(revokedCert)]; present {
			revokedCertIsIssuer := false
			for _, candidate := range candidates {
				if bytes.Equal(candidate.Raw, revokedCert.Raw) {
					revokedCertIsIssuer = true
					break
				}
			}

			if revokedCertIsIssuer {
				continue
			}
		}

		// NOTE: We have to change this to UTC time because the CRL standard
		// mandates it but Go will happily encode the CRL without this.
		newRevCert := pkix.RevokedCertificate{
			SerialNumber: revokedCert.SerialNumber,
		}
		if !revInfo.RevocationTimeUTC.IsZero() {
			newRevCert.RevocationTime = revInfo.RevocationTimeUTC
		} else {
			newRevCert.RevocationTime = time.Unix(revInfo.RevocationTime, 0).UTC()
		}

		// If we have a CertificateIssuer field on the revocation entry,
		// prefer it to manually checking each issuer signature, assuming it
		// appears valid. It's highly unlikely for two different issuers
		// to have the same id (after the first was deleted).
		if isRevInfoIssuerValid(&revInfo, issuerIDCertMap) {
			revokedCertsMap[revInfo.CertificateIssuer] = append(revokedCertsMap[revInfo.CertificateIssuer], newRevCert)
			continue

			// Otherwise, fall through and update the entry.
		}

		// Now we need to assign the revoked certificate to an issuer.
		foundParent := associateRevokedCertWithIsssuer(&revInfo, revokedCert, issuerIDCertMap)
		if !foundParent {
			// If the parent isn't found, add it to the unassigned bucket.
			unassignedCerts = append(unassignedCerts, newRevCert)
		} else {
			revokedCertsMap[revInfo.CertificateIssuer] = append(revokedCertsMap[revInfo.CertificateIssuer], newRevCert)

			// When the CertificateIssuer field wasn't found on the existing
			// entry (or was invalid), and we've found a new value for it,
			// we should update the entry to make future CRL builds faster.
			revokedEntry, err = logical.StorageEntryJSON(revokedPath+serial, revInfo)
			if err != nil {
				return nil, nil, fmt.Errorf("error creating revocation entry for existing cert: %v", serial)
			}

			err = sc.Storage.Put(sc.Context, revokedEntry)
			if err != nil {
				return nil, nil, fmt.Errorf("error updating revoked certificate at existing location: %v", serial)
			}
		}
	}

	return unassignedCerts, revokedCertsMap, nil
}

func getUnifiedRevokedCertEntries(sc *storageContext, issuerIDCertMap map[issuerID]*x509.Certificate, isDelta bool) ([]pkix.RevokedCertificate, map[issuerID][]pkix.RevokedCertificate, error) {
	// Getting unified revocation entries is a bit different than getting
	// the local ones. In particular, the full copy of the certificate is
	// unavailable, so we'll be able to avoid parsing the stored certificate,
	// at the expense of potentially having incorrect issuer mappings.
	var unassignedCerts []pkix.RevokedCertificate
	revokedCertsMap := make(map[issuerID][]pkix.RevokedCertificate)

	listingPath := unifiedRevocationReadPathPrefix
	if isDelta {
		listingPath = unifiedDeltaWALPrefix
	}

	// First, we find all clusters that have written certificates.
	clusterIds, err := sc.Storage.List(sc.Context, listingPath)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to list clusters for unified CRL building: %w", err)
	}

	// We wish to prevent duplicate revocations on separate clusters from
	// being added multiple times to the CRL. While we can't guarantee these
	// are the same certificate, it doesn't matter as (as long as they have
	// the same issuer), it'd imply issuance of two certs with the same
	// serial which'd be an intentional violation of RFC 5280 before importing
	// an issuer into Vault, and would be highly unlikely within Vault, due
	// to 120-bit random serial numbers.
	foundSerials := make(map[string]bool)

	// Then for every cluster, we find its revoked certificates...
	for _, clusterId := range clusterIds {
		if !strings.HasSuffix(clusterId, "/") {
			// No entries
			continue
		}

		clusterPath := listingPath + clusterId
		serials, err := sc.Storage.List(sc.Context, clusterPath)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to list serials in cluster (%v) for unified CRL building: %w", clusterId, err)
		}

		// At this point, we need the storage entry. Rather than using the
		// clusterPath and adding the serial, we need to use the true
		// cross-cluster revocation entry (as, our above listing might have
		// used delta WAL entires without the full revocation info).
		serialPrefix := unifiedRevocationReadPathPrefix + clusterId
		for _, serial := range serials {
			if isDelta && (serial == deltaWALLastBuildSerialName || serial == deltaWALLastRevokedSerialName) {
				// Skip our placeholder entries...
				continue
			}

			serialPath := serialPrefix + serial
			entryRaw, err := sc.Storage.Get(sc.Context, serialPath)
			if err != nil {
				return nil, nil, fmt.Errorf("failed to read unified revocation entry in cluster (%v) for unified CRL building: %w", clusterId, err)
			}
			if entryRaw == nil {
				// Skip empty entries. We'll eventually tidy them.
				continue
			}

			var xRevEntry unifiedRevocationEntry
			if err := entryRaw.DecodeJSON(&xRevEntry); err != nil {
				return nil, nil, fmt.Errorf("failed json decoding of unified revocation entry at path %v: %w ", serialPath, err)
			}

			// Convert to pkix.RevokedCertificate entries.
			var revEntry pkix.RevokedCertificate
			var ok bool
			revEntry.SerialNumber, ok = serialToBigInt(serial)
			if !ok {
				return nil, nil, fmt.Errorf("failed to encode serial for CRL building: %v", serial)
			}

			revEntry.RevocationTime = xRevEntry.RevocationTimeUTC

			if found, inFoundMap := foundSerials[normalizeSerial(serial)]; found && inFoundMap {
				// Serial has already been added to the CRL.
				continue
			}
			foundSerials[normalizeSerial(serial)] = true

			// Finally, add it to the correct mapping.
			_, present := issuerIDCertMap[xRevEntry.CertificateIssuer]
			if !present {
				unassignedCerts = append(unassignedCerts, revEntry)
			} else {
				revokedCertsMap[xRevEntry.CertificateIssuer] = append(revokedCertsMap[xRevEntry.CertificateIssuer], revEntry)
			}
		}
	}

	return unassignedCerts, revokedCertsMap, nil
}

func augmentWithRevokedIssuers(issuerIDEntryMap map[issuerID]*issuerEntry, issuerIDCertMap map[issuerID]*x509.Certificate, revokedCertsMap map[issuerID][]pkix.RevokedCertificate) error {
	// When setup our maps with the legacy CA bundle, we only have a
	// single entry here. This entry is never revoked, so the outer loop
	// will exit quickly.
	for ourIssuerID, ourIssuer := range issuerIDEntryMap {
		if !ourIssuer.Revoked {
			continue
		}

		ourCert := issuerIDCertMap[ourIssuerID]
		ourRevCert := pkix.RevokedCertificate{
			SerialNumber:   ourCert.SerialNumber,
			RevocationTime: ourIssuer.RevocationTimeUTC,
		}

		for otherIssuerID := range issuerIDEntryMap {
			if otherIssuerID == ourIssuerID {
				continue
			}

			// Find all _other_ certificates which verify this issuer,
			// allowing us to add this revoked issuer to this issuer's
			// CRL.
			otherCert := issuerIDCertMap[otherIssuerID]
			if err := ourCert.CheckSignatureFrom(otherCert); err == nil {
				// Valid signature; add our result.
				revokedCertsMap[otherIssuerID] = append(revokedCertsMap[otherIssuerID], ourRevCert)
			}
		}
	}

	return nil
}

// Builds a CRL by going through the list of revoked certificates and building
// a new CRL with the stored revocation times and serial numbers.
func buildCRL(sc *storageContext, crlInfo *crlConfig, forceNew bool, thisIssuerId issuerID, revoked []pkix.RevokedCertificate, identifier crlID, crlNumber int64, isUnified bool, isDelta bool, lastCompleteNumber int64) (*time.Time, error) {
	var revokedCerts []pkix.RevokedCertificate

	crlLifetime, err := time.ParseDuration(crlInfo.Expiry)
	if err != nil {
		return nil, errutil.InternalError{Err: fmt.Sprintf("error parsing CRL duration of %s", crlInfo.Expiry)}
	}

	if crlInfo.Disable {
		if !forceNew {
			// In the event of a disabled CRL, we'll have the next time set
			// to the zero time as a sentinel in case we get re-enabled.
			return &time.Time{}, nil
		}

		// NOTE: in this case, the passed argument (revoked) is not added
		// to the revokedCerts list. This is because we want to sign an
		// **empty** CRL (as the CRL was disabled but we've specified the
		// forceNew option). In previous versions of Vault (1.10 series and
		// earlier), we'd have queried the certs below, whereas we now have
		// an assignment from a pre-queried list.
		goto WRITE
	}

	revokedCerts = revoked

WRITE:
	signingBundle, caErr := sc.fetchCAInfoByIssuerId(thisIssuerId, CRLSigningUsage)
	if caErr != nil {
		switch caErr.(type) {
		case errutil.UserError:
			return nil, errutil.UserError{Err: fmt.Sprintf("could not fetch the CA certificate: %s", caErr)}
		default:
			return nil, errutil.InternalError{Err: fmt.Sprintf("error fetching CA certificate: %s", caErr)}
		}
	}

	now := time.Now()
	nextUpdate := now.Add(crlLifetime)

	var extensions []pkix.Extension
	if isDelta {
		ext, err := certutil.CreateDeltaCRLIndicatorExt(lastCompleteNumber)
		if err != nil {
			return nil, fmt.Errorf("could not create crl delta indicator extension: %w", err)
		}
		extensions = []pkix.Extension{ext}
	}

	revocationListTemplate := &x509.RevocationList{
		RevokedCertificates: revokedCerts,
		Number:              big.NewInt(crlNumber),
		ThisUpdate:          now,
		NextUpdate:          nextUpdate,
		SignatureAlgorithm:  signingBundle.RevocationSigAlg,
		ExtraExtensions:     extensions,
	}

	crlBytes, err := x509.CreateRevocationList(rand.Reader, revocationListTemplate, signingBundle.Certificate, signingBundle.PrivateKey)
	if err != nil {
		return nil, errutil.InternalError{Err: fmt.Sprintf("error creating new CRL: %s", err)}
	}

	writePath := "crls/" + identifier.String()
	if thisIssuerId == legacyBundleShimID {
		// Ignore the CRL ID as it won't be persisted anyways; hard-code the
		// old legacy path and allow it to be updated.
		writePath = legacyCRLPath
	} else {
		if isUnified {
			writePath = unifiedCRLPathPrefix + writePath
		}

		if isDelta {
			// Write the delta CRL to a unique storage location.
			writePath += deltaCRLPathSuffix
		}
	}

	err = sc.Storage.Put(sc.Context, &logical.StorageEntry{
		Key:   writePath,
		Value: crlBytes,
	})
	if err != nil {
		return nil, errutil.InternalError{Err: fmt.Sprintf("error storing CRL: %s", err)}
	}

	return &nextUpdate, nil
}