open-vault/sdk/helper/ocsp/client.go

// Copyright (c) 2017-2022 Snowflake Computing Inc. All rights reserved.

package ocsp

import (
	"bytes"
	"context"
	"crypto"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/asn1"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"math/big"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/hashicorp/go-hclog"
	"github.com/hashicorp/go-multierror"
	"github.com/hashicorp/go-retryablehttp"
	lru "github.com/hashicorp/golang-lru"
	"github.com/hashicorp/vault/sdk/helper/certutil"
	"golang.org/x/crypto/ocsp"
)

// FailOpenMode is OCSP fail open mode. FailOpenTrue by default and may
// set to ocspModeFailClosed for fail closed mode
type FailOpenMode uint32

type requestFunc func(method, urlStr string, body interface{}) (*retryablehttp.Request, error)

type clientInterface interface {
	Do(req *retryablehttp.Request) (*http.Response, error)
}

const (
	httpHeaderContentType   = "Content-Type"
	httpHeaderAccept        = "accept"
	httpHeaderContentLength = "Content-Length"
	httpHeaderHost          = "Host"
	ocspRequestContentType  = "application/ocsp-request"
	ocspResponseContentType = "application/ocsp-response"
)

const (
	ocspFailOpenNotSet FailOpenMode = iota
	// FailOpenTrue represents OCSP fail open mode.
	FailOpenTrue
	// FailOpenFalse represents OCSP fail closed mode.
	FailOpenFalse
)

const (
	ocspModeFailOpen   = "FAIL_OPEN"
	ocspModeFailClosed = "FAIL_CLOSED"
	ocspModeInsecure   = "INSECURE"
)

const ocspCacheKey = "ocsp_cache"

const (
	// defaultOCSPResponderTimeout is the total timeout for OCSP responder.
	defaultOCSPResponderTimeout = 10 * time.Second
)

const (
	// cacheExpire specifies cache data expiration time in seconds.
	cacheExpire = float64(24 * 60 * 60)
)

type ocspCachedResponse struct {
	time       float64
	producedAt float64
	thisUpdate float64
	nextUpdate float64
	status     ocspStatusCode
}

type Client struct {
	// caRoot includes the CA certificates.
	caRoot map[string]*x509.Certificate
	// certPool includes the CA certificates.
	certPool              *x509.CertPool
	ocspResponseCache     *lru.TwoQueueCache
	ocspResponseCacheLock sync.RWMutex
	// cacheUpdated is true if the memory cache is updated
	cacheUpdated bool
	logFactory   func() hclog.Logger
}

type ocspStatusCode int

type ocspStatus struct {
	code ocspStatusCode
	err  error
}

const (
	ocspSuccess                ocspStatusCode = 0
	ocspStatusGood             ocspStatusCode = -1
	ocspStatusRevoked          ocspStatusCode = -2
	ocspStatusUnknown          ocspStatusCode = -3
	ocspStatusOthers           ocspStatusCode = -4
	ocspFailedDecomposeRequest ocspStatusCode = -5
	ocspInvalidValidity        ocspStatusCode = -6
	ocspMissedCache            ocspStatusCode = -7
	ocspCacheExpired           ocspStatusCode = -8
)

// copied from crypto/ocsp.go
type certID struct {
	HashAlgorithm pkix.AlgorithmIdentifier
	NameHash      []byte
	IssuerKeyHash []byte
	SerialNumber  *big.Int
}

// cache key
type certIDKey struct {
	NameHash      string
	IssuerKeyHash string
	SerialNumber  string
}

// copied from crypto/ocsp
var hashOIDs = map[crypto.Hash]asn1.ObjectIdentifier{
	crypto.SHA1:   asn1.ObjectIdentifier([]int{1, 3, 14, 3, 2, 26}),
	crypto.SHA256: asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 1}),
	crypto.SHA384: asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 2}),
	crypto.SHA512: asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 3}),
}

// copied from crypto/ocsp
func getOIDFromHashAlgorithm(target crypto.Hash) (asn1.ObjectIdentifier, error) {
	for hash, oid := range hashOIDs {
		if hash == target {
			return oid, nil
		}
	}
	return nil, fmt.Errorf("no valid OID is found for the hash algorithm: %v", target)
}

func (c *Client) ClearCache() {
	c.ocspResponseCache.Purge()
}

func (c *Client) getHashAlgorithmFromOID(target pkix.AlgorithmIdentifier) crypto.Hash {
	for hash, oid := range hashOIDs {
		if oid.Equal(target.Algorithm) {
			return hash
		}
	}
	// no valid hash algorithm is found for the oid. Falling back to SHA1
	return crypto.SHA1
}

// isInValidityRange checks the validity
func isInValidityRange(currTime, nextUpdate time.Time) bool {
	return !nextUpdate.IsZero() && !currTime.After(nextUpdate)
}

func extractCertIDKeyFromRequest(ocspReq []byte) (*certIDKey, *ocspStatus) {
	r, err := ocsp.ParseRequest(ocspReq)
	if err != nil {
		return nil, &ocspStatus{
			code: ocspFailedDecomposeRequest,
			err:  err,
		}
	}

	// encode CertID, used as a key in the cache
	encodedCertID := &certIDKey{
		base64.StdEncoding.EncodeToString(r.IssuerNameHash),
		base64.StdEncoding.EncodeToString(r.IssuerKeyHash),
		r.SerialNumber.String(),
	}
	return encodedCertID, &ocspStatus{
		code: ocspSuccess,
	}
}

func (c *Client) encodeCertIDKey(certIDKeyBase64 string) (*certIDKey, error) {
	r, err := base64.StdEncoding.DecodeString(certIDKeyBase64)
	if err != nil {
		return nil, err
	}
	var cid certID
	rest, err := asn1.Unmarshal(r, &cid)
	if err != nil {
		// error in parsing
		return nil, err
	}
	if len(rest) > 0 {
		// extra bytes to the end
		return nil, err
	}
	return &certIDKey{
		base64.StdEncoding.EncodeToString(cid.NameHash),
		base64.StdEncoding.EncodeToString(cid.IssuerKeyHash),
		cid.SerialNumber.String(),
	}, nil
}

func (c *Client) checkOCSPResponseCache(encodedCertID *certIDKey, subject, issuer *x509.Certificate) (*ocspStatus, error) {
	c.ocspResponseCacheLock.RLock()
	var cacheValue *ocspCachedResponse
	v, ok := c.ocspResponseCache.Get(*encodedCertID)
	if ok {
		cacheValue = v.(*ocspCachedResponse)
	}
	c.ocspResponseCacheLock.RUnlock()

	status, err := c.extractOCSPCacheResponseValue(cacheValue, subject, issuer)
	if err != nil {
		return nil, err
	}
	if !isValidOCSPStatus(status.code) {
		c.deleteOCSPCache(encodedCertID)
	}
	return status, err
}

func (c *Client) deleteOCSPCache(encodedCertID *certIDKey) {
	c.ocspResponseCacheLock.Lock()
	c.ocspResponseCache.Remove(*encodedCertID)
	c.cacheUpdated = true
	c.ocspResponseCacheLock.Unlock()
}

func validateOCSP(ocspRes *ocsp.Response) (*ocspStatus, error) {
	curTime := time.Now()

	if ocspRes == nil {
		return nil, errors.New("OCSP Response is nil")
	}
	if !isInValidityRange(curTime, ocspRes.NextUpdate) {
		return &ocspStatus{
			code: ocspInvalidValidity,
			err:  fmt.Errorf("invalid validity: producedAt: %v, thisUpdate: %v, nextUpdate: %v", ocspRes.ProducedAt, ocspRes.ThisUpdate, ocspRes.NextUpdate),
		}, nil
	}
	return returnOCSPStatus(ocspRes), nil
}

func returnOCSPStatus(ocspRes *ocsp.Response) *ocspStatus {
	switch ocspRes.Status {
	case ocsp.Good:
		return &ocspStatus{
			code: ocspStatusGood,
			err:  nil,
		}
	case ocsp.Revoked:
		return &ocspStatus{
			code: ocspStatusRevoked,
		}
	case ocsp.Unknown:
		return &ocspStatus{
			code: ocspStatusUnknown,
			err:  errors.New("OCSP status unknown."),
		}
	default:
		return &ocspStatus{
			code: ocspStatusOthers,
			err:  fmt.Errorf("OCSP others. %v", ocspRes.Status),
		}
	}
}

// retryOCSP is the second level of retry method if the returned contents are corrupted. It often happens with OCSP
// serer and retry helps.
func (c *Client) retryOCSP(
	ctx context.Context,
	client clientInterface,
	req requestFunc,
	ocspHost *url.URL,
	headers map[string]string,
	reqBody []byte,
	issuer *x509.Certificate,
) (ocspRes *ocsp.Response, ocspResBytes []byte, ocspS *ocspStatus, retErr error) {
	doRequest := func(request *retryablehttp.Request) (*http.Response, error) {
		if request != nil {
			request = request.WithContext(ctx)
			for k, v := range headers {
				request.Header[k] = append(request.Header[k], v)
			}
		}
		res, err := client.Do(request)
		if err != nil {
			return nil, err
		}
		c.Logger().Debug("StatusCode from OCSP Server:", "statusCode", res.StatusCode)
		return res, err
	}

	for _, method := range []string{"GET", "POST"} {
		reqUrl := *ocspHost
		var body []byte

		switch method {
		case "GET":
			reqUrl.Path = reqUrl.Path + "/" + base64.StdEncoding.EncodeToString(reqBody)
		case "POST":
			body = reqBody
		default:
			// Programming error; all request/systems errors are multierror
			// and appended.
			return nil, nil, nil, fmt.Errorf("unknown request method: %v", method)
		}

		var res *http.Response
		request, err := req(method, reqUrl.String(), bytes.NewBuffer(body))
		if err != nil {
			err = fmt.Errorf("error creating %v request: %w", method, err)
			retErr = multierror.Append(retErr, err)
			continue
		}
		if res, err = doRequest(request); err != nil {
			err = fmt.Errorf("error doing %v request: %w", method, err)
			retErr = multierror.Append(retErr, err)
			continue
		} else {
			defer res.Body.Close()
		}

		if res.StatusCode != http.StatusOK {
			err = fmt.Errorf("HTTP code is not OK on %v request. %v: %v", method, res.StatusCode, res.Status)
			retErr = multierror.Append(retErr, err)
			continue
		}

		ocspResBytes, err = io.ReadAll(res.Body)
		if err != nil {
			err = fmt.Errorf("error reading %v request body: %w", method, err)
			retErr = multierror.Append(retErr, err)
			continue
		}

		// Reading an OCSP response shouldn't be fatal. A misconfigured
		// endpoint might return invalid results for e.g., GET but return
		// valid results for POST on retry. This could happen if e.g., the
		// server responds with JSON.
		ocspRes, err = ocsp.ParseResponse(ocspResBytes, issuer)
		if err != nil {
			err = fmt.Errorf("error parsing %v OCSP response: %w", method, err)
			retErr = multierror.Append(retErr, err)
			continue
		}

		// While we haven't validated the signature on the OCSP response, we
		// got what we presume is a definitive answer and simply changing
		// methods will likely not help us in that regard. Use this status
		// to return without retrying another method, when it looks definitive.
		//
		// We don't accept ocsp.Unknown here: presumably, we could've hit a CDN
		// with static mapping of request->responses, with a default "unknown"
		// handler for everything else. By retrying here, we use POST, which
		// could hit a live OCSP server with fresher data than the cached CDN.
		if ocspRes.Status == ocsp.Good || ocspRes.Status == ocsp.Revoked {
			break
		}

		// Here, we didn't have a valid response. Even though we didn't get an
		// error, we should inform the user that this (valid-looking) response
		// wasn't utilized.
		err = fmt.Errorf("fetched %v OCSP response of status %v; wanted either good (%v) or revoked (%v)", method, ocspRes.Status, ocsp.Good, ocsp.Revoked)
		retErr = multierror.Append(retErr, err)
	}

	if ocspRes != nil && ocspResBytes != nil {
		// Clear retErr, because we have one parseable-but-maybe-not-quite-correct
		// OCSP response.
		retErr = nil
		ocspS = &ocspStatus{
			code: ocspSuccess,
		}
	}

	return
}

// GetRevocationStatus checks the certificate revocation status for subject using issuer certificate.
func (c *Client) GetRevocationStatus(ctx context.Context, subject, issuer *x509.Certificate, conf *VerifyConfig) (*ocspStatus, error) {
	status, ocspReq, encodedCertID, err := c.validateWithCache(subject, issuer)
	if err != nil {
		return nil, err
	}
	if isValidOCSPStatus(status.code) {
		return status, nil
	}
	if ocspReq == nil || encodedCertID == nil {
		return status, nil
	}
	c.Logger().Debug("cache missed", "server", subject.OCSPServer)
	if len(subject.OCSPServer) == 0 && len(conf.OcspServersOverride) == 0 {
		return nil, fmt.Errorf("no OCSP responder URL: subject: %v", subject.Subject)
	}
	ocspHosts := subject.OCSPServer
	if len(conf.OcspServersOverride) > 0 {
		ocspHosts = conf.OcspServersOverride
	}

	var wg sync.WaitGroup

	ocspStatuses := make([]*ocspStatus, len(ocspHosts))
	ocspResponses := make([]*ocsp.Response, len(ocspHosts))
	errors := make([]error, len(ocspHosts))

	for i, ocspHost := range ocspHosts {
		u, err := url.Parse(ocspHost)
		if err != nil {
			return nil, err
		}

		hostname := u.Hostname()

		headers := make(map[string]string)
		headers[httpHeaderContentType] = ocspRequestContentType
		headers[httpHeaderAccept] = ocspResponseContentType
		headers[httpHeaderContentLength] = strconv.Itoa(len(ocspReq))
		headers[httpHeaderHost] = hostname
		timeout := defaultOCSPResponderTimeout

		ocspClient := retryablehttp.NewClient()
		ocspClient.HTTPClient.Timeout = timeout
		ocspClient.HTTPClient.Transport = newInsecureOcspTransport(conf.ExtraCas)

		doRequest := func() error {
			if conf.QueryAllServers {
				defer wg.Done()
			}
			ocspRes, _, ocspS, err := c.retryOCSP(
				ctx, ocspClient, retryablehttp.NewRequest, u, headers, ocspReq, issuer)
			ocspResponses[i] = ocspRes
			if err != nil {
				errors[i] = err
				return err
			}
			if ocspS.code != ocspSuccess {
				ocspStatuses[i] = ocspS
				return nil
			}

			ret, err := validateOCSP(ocspRes)
			if err != nil {
				errors[i] = err
				return err
			}
			if isValidOCSPStatus(ret.code) {
				ocspStatuses[i] = ret
			}
			return nil
		}
		if conf.QueryAllServers {
			wg.Add(1)
			go doRequest()
		} else {
			err = doRequest()
			if err == nil {
				break
			}
		}
	}
	if conf.QueryAllServers {
		wg.Wait()
	}
	// Good by default
	var ret *ocspStatus
	ocspRes := ocspResponses[0]
	var firstError error
	for i := range ocspHosts {
		if errors[i] != nil {
			if firstError == nil {
				firstError = errors[i]
			}
		} else if ocspStatuses[i] != nil {
			switch ocspStatuses[i].code {
			case ocspStatusRevoked:
				ret = ocspStatuses[i]
				ocspRes = ocspResponses[i]
				break
			case ocspStatusGood:
				// Use this response only if we don't have a status already, or if what we have was unknown
				if ret == nil || ret.code == ocspStatusUnknown {
					ret = ocspStatuses[i]
					ocspRes = ocspResponses[i]
				}
			case ocspStatusUnknown:
				if ret == nil {
					// We may want to use this as the overall result
					ret = ocspStatuses[i]
					ocspRes = ocspResponses[i]
				}
			}
		}
	}

	// If no server reported the cert revoked, but we did have an error, report it
	if (ret == nil || ret.code == ocspStatusUnknown) && firstError != nil {
		return nil, firstError
	}
	// otherwise ret should contain a response for the overall request

	if !isValidOCSPStatus(ret.code) {
		return ret, nil
	}
	v := ocspCachedResponse{
		status:     ret.code,
		time:       float64(time.Now().UTC().Unix()),
		producedAt: float64(ocspRes.ProducedAt.UTC().Unix()),
		thisUpdate: float64(ocspRes.ThisUpdate.UTC().Unix()),
		nextUpdate: float64(ocspRes.NextUpdate.UTC().Unix()),
	}

	c.ocspResponseCacheLock.Lock()
	c.ocspResponseCache.Add(*encodedCertID, &v)
	c.cacheUpdated = true
	c.ocspResponseCacheLock.Unlock()
	return ret, nil
}

func isValidOCSPStatus(status ocspStatusCode) bool {
	return status == ocspStatusGood || status == ocspStatusRevoked || status == ocspStatusUnknown
}

type VerifyConfig struct {
	OcspEnabled         bool
	ExtraCas            []*x509.Certificate
	OcspServersOverride []string
	OcspFailureMode     FailOpenMode
	QueryAllServers     bool
}

// VerifyLeafCertificate verifies just the subject against it's direct issuer
func (c *Client) VerifyLeafCertificate(ctx context.Context, subject, issuer *x509.Certificate, conf *VerifyConfig) error {
	results, err := c.GetRevocationStatus(ctx, subject, issuer, conf)
	if err != nil {
		return err
	}
	if results.code == ocspStatusGood {
		return nil
	} else {
		serial := issuer.SerialNumber
		serialHex := strings.TrimSpace(certutil.GetHexFormatted(serial.Bytes(), ":"))
		if results.code == ocspStatusRevoked {
			return fmt.Errorf("certificate with serial number %s has been revoked", serialHex)
		} else if conf.OcspFailureMode == FailOpenFalse {
			return fmt.Errorf("unknown OCSP status for cert with serial number %s", strings.TrimSpace(certutil.GetHexFormatted(serial.Bytes(), ":")))
		} else {
			c.Logger().Warn("could not validate OCSP status for cert, but continuing in fail open mode", "serial", serialHex)
		}
	}
	return nil
}

// VerifyPeerCertificate verifies all of certificate revocation status
func (c *Client) VerifyPeerCertificate(ctx context.Context, verifiedChains [][]*x509.Certificate, conf *VerifyConfig) error {
	for i := 0; i < len(verifiedChains); i++ {
		// Certificate signed by Root CA. This should be one before the last in the Certificate Chain
		numberOfNoneRootCerts := len(verifiedChains[i]) - 1
		if !verifiedChains[i][numberOfNoneRootCerts].IsCA || string(verifiedChains[i][numberOfNoneRootCerts].RawIssuer) != string(verifiedChains[i][numberOfNoneRootCerts].RawSubject) {
			// Check if the last Non Root Cert is also a CA or is self signed.
			// if the last certificate is not, add it to the list
			rca := c.caRoot[string(verifiedChains[i][numberOfNoneRootCerts].RawIssuer)]
			if rca == nil {
				return fmt.Errorf("failed to find root CA. pkix.name: %v", verifiedChains[i][numberOfNoneRootCerts].Issuer)
			}
			verifiedChains[i] = append(verifiedChains[i], rca)
			numberOfNoneRootCerts++
		}
		results, err := c.GetAllRevocationStatus(ctx, verifiedChains[i], conf)
		if err != nil {
			return err
		}
		if r := c.canEarlyExitForOCSP(results, numberOfNoneRootCerts, conf); r != nil {
			return r.err
		}
	}

	return nil
}

func (c *Client) canEarlyExitForOCSP(results []*ocspStatus, chainSize int, conf *VerifyConfig) *ocspStatus {
	msg := ""
	if conf.OcspFailureMode == FailOpenFalse {
		// Fail closed. any error is returned to stop connection
		for _, r := range results {
			if r.err != nil {
				return r
			}
		}
	} else {
		// Fail open and all results are valid.
		allValid := len(results) == chainSize
		for _, r := range results {
			if !isValidOCSPStatus(r.code) {
				allValid = false
				break
			}
		}
		for _, r := range results {
			if allValid && r.code == ocspStatusRevoked {
				return r
			}
			if r != nil && r.code != ocspStatusGood && r.err != nil {
				msg += "" + r.err.Error()
			}
		}
	}
	if len(msg) > 0 {
		c.Logger().Warn(
			"OCSP is set to fail-open, and could not retrieve OCSP based revocation checking but proceeding.", "detail", msg)
	}
	return nil
}

func (c *Client) validateWithCacheForAllCertificates(verifiedChains []*x509.Certificate) (bool, error) {
	n := len(verifiedChains) - 1
	for j := 0; j < n; j++ {
		subject := verifiedChains[j]
		issuer := verifiedChains[j+1]
		status, _, _, err := c.validateWithCache(subject, issuer)
		if err != nil {
			return false, err
		}
		if !isValidOCSPStatus(status.code) {
			return false, nil
		}
	}
	return true, nil
}

func (c *Client) validateWithCache(subject, issuer *x509.Certificate) (*ocspStatus, []byte, *certIDKey, error) {
	ocspReq, err := ocsp.CreateRequest(subject, issuer, &ocsp.RequestOptions{})
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to create OCSP request from the certificates: %v", err)
	}
	encodedCertID, ocspS := extractCertIDKeyFromRequest(ocspReq)
	if ocspS.code != ocspSuccess {
		return nil, nil, nil, fmt.Errorf("failed to extract CertID from OCSP Request: %v", err)
	}
	status, err := c.checkOCSPResponseCache(encodedCertID, subject, issuer)
	if err != nil {
		return nil, nil, nil, err
	}
	return status, ocspReq, encodedCertID, nil
}

func (c *Client) GetAllRevocationStatus(ctx context.Context, verifiedChains []*x509.Certificate, conf *VerifyConfig) ([]*ocspStatus, error) {
	_, err := c.validateWithCacheForAllCertificates(verifiedChains)
	if err != nil {
		return nil, err
	}
	n := len(verifiedChains) - 1
	results := make([]*ocspStatus, n)
	for j := 0; j < n; j++ {
		results[j], err = c.GetRevocationStatus(ctx, verifiedChains[j], verifiedChains[j+1], conf)
		if err != nil {
			return nil, err
		}
		if !isValidOCSPStatus(results[j].code) {
			return results, nil
		}
	}
	return results, nil
}

// verifyPeerCertificateSerial verifies the certificate revocation status in serial.
func (c *Client) verifyPeerCertificateSerial(conf *VerifyConfig) func(_ [][]byte, verifiedChains [][]*x509.Certificate) (err error) {
	return func(_ [][]byte, verifiedChains [][]*x509.Certificate) error {
		return c.VerifyPeerCertificate(context.TODO(), verifiedChains, conf)
	}
}

func (c *Client) extractOCSPCacheResponseValueWithoutSubject(cacheValue ocspCachedResponse) (*ocspStatus, error) {
	return c.extractOCSPCacheResponseValue(&cacheValue, nil, nil)
}

func (c *Client) extractOCSPCacheResponseValue(cacheValue *ocspCachedResponse, subject, issuer *x509.Certificate) (*ocspStatus, error) {
	subjectName := "Unknown"
	if subject != nil {
		subjectName = subject.Subject.CommonName
	}

	curTime := time.Now()
	if cacheValue == nil {
		return &ocspStatus{
			code: ocspMissedCache,
			err:  fmt.Errorf("miss cache data. subject: %v", subjectName),
		}, nil
	}
	currentTime := float64(curTime.UTC().Unix())
	if currentTime-cacheValue.time >= cacheExpire {
		return &ocspStatus{
			code: ocspCacheExpired,
			err: fmt.Errorf("cache expired. current: %v, cache: %v",
				time.Unix(int64(currentTime), 0).UTC(), time.Unix(int64(cacheValue.time), 0).UTC()),
		}, nil
	}

	return validateOCSP(&ocsp.Response{
		ProducedAt: time.Unix(int64(cacheValue.producedAt), 0).UTC(),
		ThisUpdate: time.Unix(int64(cacheValue.thisUpdate), 0).UTC(),
		NextUpdate: time.Unix(int64(cacheValue.nextUpdate), 0).UTC(),
		Status:     int(cacheValue.status),
	})
}

/*
// writeOCSPCache writes a OCSP Response cache
func (c *Client) writeOCSPCache(ctx context.Context, storage logical.Storage) error {
	c.Logger().Debug("writing OCSP Response cache")
	t := time.Now()
	m := make(map[string][]interface{})
	keys := c.ocspResponseCache.Keys()
	if len(keys) > persistedCacheSize {
		keys = keys[:persistedCacheSize]
	}
	for _, k := range keys {
		e, ok := c.ocspResponseCache.Get(k)
		if ok {
			entry := e.(*ocspCachedResponse)
			// Don't store if expired
			if isInValidityRange(t, time.Unix(int64(entry.thisUpdate), 0), time.Unix(int64(entry.nextUpdate), 0)) {
				key := k.(certIDKey)
				cacheKeyInBase64, err := decodeCertIDKey(&key)
				if err != nil {
					return err
				}
				m[cacheKeyInBase64] = []interface{}{entry.status, entry.time, entry.producedAt, entry.thisUpdate, entry.nextUpdate}
			}
		}
	}

	v, err := jsonutil.EncodeJSONAndCompress(m, nil)
	if err != nil {
		return err
	}
	entry := logical.StorageEntry{
		Key:   ocspCacheKey,
		Value: v,
	}
	return storage.Put(ctx, &entry)
}

// readOCSPCache reads a OCSP Response cache from storage
func (c *Client) readOCSPCache(ctx context.Context, storage logical.Storage) error {
	c.Logger().Debug("reading OCSP Response cache")

	entry, err := storage.Get(ctx, ocspCacheKey)
	if err != nil {
		return err
	}
	if entry == nil {
		return nil
	}
	var untypedCache map[string][]interface{}

	err = jsonutil.DecodeJSON(entry.Value, &untypedCache)
	if err != nil {
		return errors.New("failed to unmarshal OCSP cache")
	}

	for k, v := range untypedCache {
		key, err := c.encodeCertIDKey(k)
		if err != nil {
			return err
		}
		var times [4]float64
		for i, t := range v[1:] {
			if jn, ok := t.(json.Number); ok {
				times[i], err = jn.Float64()
				if err != nil {
					return err
				}
			} else {
				times[i] = t.(float64)
			}
		}
		var status int
		if jn, ok := v[0].(json.Number); ok {
			s, err := jn.Int64()
			if err != nil {
				return err
			}
			status = int(s)
		} else {
			status = v[0].(int)
		}

		c.ocspResponseCache.Add(*key, &ocspCachedResponse{
			status:     ocspStatusCode(status),
			time:       times[0],
			producedAt: times[1],
			thisUpdate: times[2],
			nextUpdate: times[3],
		})
	}

	return nil
}
*/

func New(logFactory func() hclog.Logger, cacheSize int) *Client {
	if cacheSize < 100 {
		cacheSize = 100
	}
	cache, _ := lru.New2Q(cacheSize)
	c := Client{
		caRoot:            make(map[string]*x509.Certificate),
		ocspResponseCache: cache,
		logFactory:        logFactory,
	}

	return &c
}

func (c *Client) Logger() hclog.Logger {
	return c.logFactory()
}

// insecureOcspTransport is the transport object that doesn't do certificate revocation check.
func newInsecureOcspTransport(extraCas []*x509.Certificate) *http.Transport {
	// Get the SystemCertPool, continue with an empty pool on error
	rootCAs, _ := x509.SystemCertPool()
	if rootCAs == nil {
		rootCAs = x509.NewCertPool()
	}
	for _, c := range extraCas {
		rootCAs.AddCert(c)
	}
	config := &tls.Config{
		RootCAs: rootCAs,
	}
	return &http.Transport{
		MaxIdleConns:    10,
		IdleConnTimeout: 30 * time.Minute,
		Proxy:           http.ProxyFromEnvironment,
		DialContext: (&net.Dialer{
			Timeout:   30 * time.Second,
			KeepAlive: 30 * time.Second,
		}).DialContext,
		TLSClientConfig: config,
	}
}

// NewTransport includes the certificate revocation check with OCSP in sequential.
func (c *Client) NewTransport(conf *VerifyConfig) *http.Transport {
	rootCAs := c.certPool
	if rootCAs == nil {
		rootCAs, _ = x509.SystemCertPool()
	}
	if rootCAs == nil {
		rootCAs = x509.NewCertPool()
	}
	for _, c := range conf.ExtraCas {
		rootCAs.AddCert(c)
	}
	return &http.Transport{
		TLSClientConfig: &tls.Config{
			RootCAs:               rootCAs,
			VerifyPeerCertificate: c.verifyPeerCertificateSerial(conf),
		},
		MaxIdleConns:    10,
		IdleConnTimeout: 30 * time.Minute,
		Proxy:           http.ProxyFromEnvironment,
		DialContext: (&net.Dialer{
			Timeout:   30 * time.Second,
			KeepAlive: 30 * time.Second,
		}).DialContext,
	}
}

/*
func (c *Client) WriteCache(ctx context.Context, storage logical.Storage) error {
	c.ocspResponseCacheLock.Lock()
	defer c.ocspResponseCacheLock.Unlock()
	if c.cacheUpdated {
		err := c.writeOCSPCache(ctx, storage)
		if err == nil {
			c.cacheUpdated = false
		}
		return err
	}
	return nil
}

func (c *Client) ReadCache(ctx context.Context, storage logical.Storage) error {
	c.ocspResponseCacheLock.Lock()
	defer c.ocspResponseCacheLock.Unlock()
	return c.readOCSPCache(ctx, storage)
}
*/
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