1---
2layout: docs
3page_title: TLS Certificates - Auth Methods
4description: >-
5  The "cert" auth method allows users to authenticate with Vault using TLS
6  client certificates.
7---
8
9# TLS Certificates Auth Method
10
11The `cert` auth method allows authentication using SSL/TLS client certificates
12which are either signed by a CA or self-signed.
13
14The trusted certificates and CAs are configured directly to the auth method
15using the `certs/` path. This method cannot read trusted certificates from an
16external source.
17
18CA certificates are associated with a role; role names and CRL names are normalized to
19lower-case.
20
21Please note that to use this auth method, `tls_disable` must be false in the Vault
22configuration. This is because the certificates are sent through TLS communication itself.
23
24## Revocation Checking
25
26Since Vault 0.4, the method supports revocation checking.
27
28An authorised user can submit PEM-formatted CRLs identified by a given name;
29these can be updated or deleted at will. (Note: Vault **does not** fetch CRLs;
30the CRLs themselves and any updates must be pushed into Vault when desired,
31such as via a `cron` job that fetches them from the source and pushes them into
32Vault.)
33
34When there are CRLs present, at the time of client authentication:
35
36- If the client presents any chain where no certificate in the chain matches a
37  revoked serial number, authentication is allowed
38
39- If there is no chain presented by the client without a revoked serial number,
40  authentication is denied
41
42This method provides good security while also allowing for flexibility. For
43instance, if an intermediate CA is going to be retired, a client can be
44configured with two certificate chains: one that contains the initial
45intermediate CA in the path, and the other that contains the replacement. When
46the initial intermediate CA is revoked, the chain containing the replacement
47will still allow the client to successfully authenticate.
48
49**N.B.**: Matching is performed by _serial number only_. For most CAs,
50including Vault's `pki` method, multiple CRLs can successfully be used as
51serial numbers are globally unique. However, since RFCs only specify that
52serial numbers must be unique per-CA, some CAs issue serial numbers in-order,
53which may cause clashes if attempting to use CRLs from two such CAs in the same
54mount of the method. The workaround here is to mount multiple copies of the
55`cert` method, configure each with one CA/CRL, and have clients connect to the
56appropriate mount.
57
58In addition, since the method does not fetch the CRLs itself, the CRL's
59designated time to next update is not considered. If a CRL is no longer in use,
60it is up to the administrator to remove it from the method.
61
62## Authentication
63
64### Via the CLI
65
66The below authenticates against the `web` cert role by presenting a certificate
67(`cert.pem`) and key (`key.pem`) signed by the CA associated with the `web` cert
68role. Note that the name `web` ties to the configuration example below writing
69to a path of `auth/cert/certs/web`. If a certificate role name is not specified,
70the auth method will try to authenticate against all trusted certificates.
71
72~> **NOTE** The `-ca-cert` value used here is for the Vault TLS Listener CA
73certificate, not the CA that issued the client authentication certificate. This
74can be omitted if the CA used to issue the Vault server certificate is trusted
75by the local system executing this command.
76
77```shell-session
78$ vault login \
79    -method=cert \
80    -ca-cert=vault-ca.pem \
81    -client-cert=cert.pem \
82    -client-key=key.pem \
83    name=web
84```
85
86### Via the API
87
88The endpoint for the login is `/login`. The client simply connects with their
89TLS certificate and when the login endpoint is hit, the auth method will
90determine if there is a matching trusted certificate to authenticate the client.
91Optionally, you may specify a single certificate role to authenticate against.
92
93~> **NOTE** The `--cacert` value used here is for the Vault TLS Listener CA
94certificate, not the CA that issued the client authentication certificate. This
95can be omitted if the CA used to issue the Vault server certificate is trusted
96by the local system executing this command.
97
98```shell-session
99$ curl \
100    --request POST \
101    --cacert vault-ca.pem \
102    --cert cert.pem \
103    --key key.pem \
104    --data '{"name": "web"}' \
105    https://127.0.0.1:8200/v1/auth/cert/login
106```
107
108## Configuration
109
110Auth methods must be configured in advance before users or machines can
111authenticate. These steps are usually completed by an operator or configuration
112management tool.
113
1141. Enable the certificate auth method:
115
116   ```text
117   $ vault auth enable cert
118   ```
119
1201. Configure it with trusted certificates that are allowed to authenticate:
121
122   ```text
123   $ vault write auth/cert/certs/web \
124       display_name=web \
125       policies=web,prod \
126       certificate=@web-cert.pem \
127       ttl=3600
128   ```
129
130   This creates a new trusted certificate "web" with same display name and the
131   "web" and "prod" policies. The certificate (public key) used to verify
132   clients is given by the "web-cert.pem" file. Lastly, an optional `ttl` value
133   can be provided in seconds to limit the lease duration.
134
135## API
136
137The TLS Certificate auth method has a full HTTP API. Please see the
138[TLS Certificate API](/api/auth/cert) for more details.
139