# OCSP Stapling

_Supported since NATS Server version 2.3_

[OCSP Stapling](https://en.wikipedia.org/wiki/OCSP_stapling) is honored by default for certificates that have 
the [status_request Must-Staple flag](https://datatracker.ietf.org/doc/html/rfc6961).

When a certificate is configured with OCSP Must-Staple, the NATS Server will fetch staples from the configured OCSP responder URL
that is present in a certificate. For example, given a certificate with the following configuration:
               
```
[ ext_ca ]
...                                                                           
authorityInfoAccess = OCSP;URI:http://ocsp.example.net:80
tlsfeature = status_request
...
```

The NATS server will make a request to the OCSP responder to fetch a new staple which will be then presented to
any TLS connection that is accepted by the server during the TLS handshake.

OCSP Stapling can be explicitly enabled or disabled in the NATS Server by setting the following flag in the NATS configuration file:

```hcl
ocsp: false
```

**Note**: When OCSP Stapling is disabled, the NATS Server will not request staples even if the certificate has
the Must-Staple flag.

## Advanced configuration

By default, the NATS Server will be running in OCSP `auto` mode.  In this mode the server will only fetch 
staples when the Must-Staple flag is configured in the certificate.
                     
There are a other different OCSP modes that control the behavior on whether OCSP should be enforced and server
should shutdown if the cert runs with a revoked staple:
                     
| Mode   | Description                                                           | Server shutdowns when revoked |
| --------- | ---- | ----- |
| auto   | Enables OCSP Stapling when it has the must staple/status_request flag | No                            |
| must   | Enables OCSP Staping when it has the must staple/status_request flag  | Yes                           |
| always | Enables OCSP Stapling for all certificates                            | Yes                           |
| never  | Disables OCSP Stapling even if must staple flag is present (same as `ocsp: false` | No                            |

For example, in the following configuration OCSP, the mode is set to `must`. This means that staples will be fetched only for certificates
that have the Must-Staple flag enabled as well, but in case of revokation the server will shutdown rather than run with a revoked staple.  
In this configuration, the `url` will also override OCSP responder URL that may have been configured in
the certificate.

```hcl
ocsp {
  mode: must
  url: "http://ocsp.example.net"
}
```

In case staples are always required regardless of the configuration of the certificate, then this can be enforced as follows:
                     
```hcl
ocsp {
  mode: always
  url: "http://ocsp.example.net"
}
```

## Caching of staples

When a `store_dir` is configured in the NATS Server, the directory will be used to cache staples on disk
to allow the server to resume in case of restarts without having to make another request to the OCSP responder
in case the staple is still valid.
                    
```hcl
store_dir: "/path/to/store/dir"
tls {
	cert_file: "configs/certs/ocsp/server-status-request-url.pem"
	key_file: "configs/certs/ocsp/server-status-request-url-key.pem"
	ca_file: "configs/certs/ocsp/ca-cert.pem"
	timeout: 5
}
```

If JetStream is enabled, then the same `store_dir` will be reused and disk caching will be automatically enabled.