open-vault/website/source/docs/auth/cert.html.md

layout	page_title	sidebar_current	description
docs	Auth Backend: TLS Certificates	docs-auth-cert	The "cert" auth backend allows users to authenticate with Vault using TLS client certificates.

Auth Backend: TLS Certificates

Name: cert

The "cert" auth backend allows authentication using SSL/TLS client certificates which are either signed by a CA or self-signed.

The trusted certificates and CAs are configured directly to the auth backend using the certs/ path. This backend cannot read trusted certificates from an external source.

CA certs are associated with a role; role names and CRL names are normalized to lower-case.

Revocation Checking

Since Vault 0.4, the backend supports revocation checking.

An authorised user can submit PEM-formatted CRLs identified by a given name; these can be updated or deleted at will. (Note: Vault does not fetch CRLs; the CRLs themselves and any updates must be pushed into Vault when desired, such as via a cron job that fetches them from the source and pushes them into Vault.)

When there are CRLs present, at the time of client authentication:

• If the client presents any chain where no certificate in the chain matches a revoked serial number, authentication is allowed
• If there is no chain presented by the client without a revoked serial number, authentication is denied

This method provides good security while also allowing for flexibility. For instance, if an intermediate CA is going to be retired, a client can be configured with two certificate chains: one that contains the initial intermediate CA in the path, and the other that contains the replacement. When the initial intermediate CA is revoked, the chain containing the replacement will still allow the client to successfully authenticate.

N.B.: Matching is performed by serial number only. For most CAs, including Vault's pki backend, multiple CRLs can successfully be used as serial numbers are globally unique. However, since RFCs only specify that serial numbers must be unique per-CA, some CAs issue serial numbers in-order, which may cause clashes if attempting to use CRLs from two such CAs in the same mount of the backend. The workaround here is to mount multiple copies of the cert backend, configure each with one CA/CRL, and have clients connect to the appropriate mount.

In addition, since the backend does not fetch the CRLs itself, the CRL's designated time to next update is not considered. If a CRL is no longer in use, it is up to the administrator to remove it from the backend.

Authentication

Via the CLI

The below requires Vault to present a certificate signed by ca.pem and presents cert.pem (using key.pem) to authenticate against the web cert role. If a certificate role name is not specified, the auth backend will try to authenticate against all trusted certificates.

$ vault auth -method=cert \
    -ca-cert=ca.pem -client-cert=cert.pem -client-key=key.pem \
    name=web

Via the API

The endpoint for the login is /login. The client simply connects with their TLS certificate and when the login endpoint is hit, the auth backend will determine if there is a matching trusted certificate to authenticate the client. Optionally, you may specify a single certificate role to authenticate against.

$ curl --cacert ca.pem --cert cert.pem --key key.pem -d name=web \
    $VAULT_ADDR/v1/auth/cert/login -XPOST

Configuration

First, you must enable the certificate auth backend:

$ vault auth-enable cert
Successfully enabled 'cert' at 'cert'!

Now when you run vault auth -methods, the certificate backend is available:

Path       Type      Description
cert/      cert
token/     token     token based credentials

To use the "cert" auth backend, an operator must configure it with trusted certificates that are allowed to authenticate. An example is shown below. Use vault path-help for more details.

$ vault write auth/cert/certs/web \
    display_name=web \
    policies=web,prod \
    certificate=@web-cert.pem \
    ttl=3600
...

The above creates a new trusted certificate "web" with same display name and the "web" and "prod" policies. The certificate (public key) used to verify clients is given by the "web-cert.pem" file. Lastly, an optional ttl value can be provided in seconds to limit the lease duration.

Via the API

The token is set directly as a header for the HTTP API. The name of the header should be "X-Vault-Token" and the value should be the token.

API

The TLS Certificate authentication backend has a full HTTP API. Please see the TLS Certificate API for more details.