---
layout: docs
page_title: TLS Certificates - Auth Methods
sidebar_title: TLS Certificates
description: >-
  The "cert" auth method allows users to authenticate with Vault using TLS
  client certificates.
---

# TLS Certificates Auth Method

The `cert` auth method 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 method
using the `certs/` path. This method cannot read trusted certificates from an
external source.

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

Please note that to use this auth method, `tls_disable` must be false in the Vault
configuration. This is because the certificates are sent through TLS communication itself.

## Revocation Checking

Since Vault 0.4, the method 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` method, 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 method. The workaround here is to mount multiple copies of the
`cert` method, configure each with one CA/CRL, and have clients connect to the
appropriate mount.

In addition, since the method 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 method.

## Authentication

### Via the CLI

The below authenticates against the `web` cert role by presenting a certificate
(`cert.pem`) and key (`key.pem`) signed by the CA associated with the `web` cert
role. Note that the name `web` ties to the configuration example below writing
to a path of `auth/cert/certs/web`. If a certificate role name is not specified,
the auth method will try to authenticate against all trusted certificates.

~> **NOTE** The `-ca-cert` value used here is for the Vault TLS Listener CA
certificate, not the CA that issued the client authentication certificate. This
can be omitted if the CA used to issue the Vault server certificate is trusted
by the local system executing this command.

```shell-session
$ vault login \
    -method=cert \
    -ca-cert=vault-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 method will
determine if there is a matching trusted certificate to authenticate the client.
Optionally, you may specify a single certificate role to authenticate against.

~> **NOTE** The `--cacert` value used here is for the Vault TLS Listener CA
certificate, not the CA that issued the client authentication certificate. This
can be omitted if the CA used to issue the Vault server certificate is trusted
by the local system executing this command.

```shell-session
$ curl \
    --request POST \
    --cacert vault-ca.pem \
    --cert cert.pem \
    --key key.pem \
    --data '{"name": "web"}' \
    https://127.0.0.1:8200/v1/auth/cert/login
```

## Configuration

Auth methods must be configured in advance before users or machines can
authenticate. These steps are usually completed by an operator or configuration
management tool.

1. Enable the certificate auth method:

   ```text
   $ vault auth enable cert
   ```

1. Configure it with trusted certificates that are allowed to authenticate:

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

   This 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.

## API

The TLS Certificate auth method has a full HTTP API. Please see the
[TLS Certificate API](/api/auth/cert) for more details.