> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-detect-table-modification.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

> Documentation for Ssl X509

# SSL X.509 certificate authentication

export const CloudNotSupportedBadge = () => {
  return <div className="cloudNotSupportedBadge">
            <div className="cloudNotSupportedIcon">
            <svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
                <path strokeWidth="1.5" d="M6.33366 12.6666L12.3739 12.6667C13.6593 12.6667 14.7073 11.6187 14.7073 10.3334C14.7073 9.04804 13.6593 8.00003 12.3739 8.00003C12.3739 8.00003 12.3337 7.66659 12.0003 7.33325M10.667 5.33322C8.00033 2.33325 4.45395 4.78537 4.14195 6.68203C2.55728 6.7627 1.29395 8.06203 1.29395 9.6667C1.29395 11.3234 2.66699 12.6666 4.00033 12.6666" stroke="currentColor" strokeLinecap="round" strokeLinejoin="round" />
                <path strokeWidth="1.5" d="M2.66699 14L12.0003 4.66663" stroke="currentColor" strokeLinecap="round" strokeLinejoin="round" />
            </svg>

        </div>
            Not supported in ClickHouse Cloud
        </div>;
};

<CloudNotSupportedBadge />

<Note>
  This page isn't applicable to [ClickHouse Cloud](https://clickhouse.com/cloud). The feature documented here isn't available in ClickHouse Cloud services.
  See the ClickHouse [Cloud Compatibility](/products/cloud/guides/cloud-compatibility) guide for more information.
</Note>

[SSL 'strict' option](/reference/settings/server-settings/settings#openssl) enables mandatory certificate validation for the incoming connections. In this case, only connections with trusted certificates can be established. Connections with untrusted certificates will be rejected. Thus, certificate validation allows to uniquely authenticate an incoming connection. `Common Name` or `subjectAltName extension` field of the certificate is used to identify the connected user. `subjectAltName extension` supports the usage of one wildcard '\*' in the server configuration. This allows to associate multiple certificates with the same user. Additionally, reissuing and revoking of the certificates does not affect the ClickHouse configuration.

To enable SSL certificate authentication, a list of `Common Name`'s or `Subject Alt Name`'s for each ClickHouse user must be specified in the settings file `users.xml `:

**Example**

```xml theme={null}
<clickhouse>
    <!- ... -->
    <users>
        <user_name_1>
            <ssl_certificates>
                <common_name>host.domain.com:example_user</common_name>
                <common_name>host.domain.com:example_user_dev</common_name>
                <!-- More names -->
            </ssl_certificates>
            <!-- Other settings -->
        </user_name_1>
        <user_name_2>
            <ssl_certificates>
                <subject_alt_name>DNS:host.domain.com</subject_alt_name>
                <!-- More names -->
            </ssl_certificates>
            <!-- Other settings -->
        </user_name_2>
        <user_name_3>
            <ssl_certificates>
                <!-- Wildcard support -->
                <subject_alt_name>URI:spiffe://foo.com/*/bar</subject_alt_name>
            </ssl_certificates>
        </user_name_3>
    </users>
</clickhouse>
```

For the SSL [`chain of trust`](https://en.wikipedia.org/wiki/Chain_of_trust) to work correctly, it is also important to make sure that the [`caConfig`](/reference/settings/server-settings/settings#openssl) parameter is configured properly.