DOC-4692 RS: Create certificate-based authentication page (#1511)

Author: rrelledge

content/operate/rs/security/certificates/certificate-based-authentication.md

@@ -0,0 +1,116 @@
+---
+Title: Certificate-based authentication
+alwaysopen: false
+categories:
+- docs
+- operate
+- rs
+description: Certificate-based authentication allows secure, passwordless access to the REST API and databases.
+linkTitle: Certificate-based authentication 
+weight: 70
+---
+
+You can set up certificate-based authentication for specific users to enable secure, passwordless access to the Redis Enterprise Software [REST API]({{<relref "/operate/rs/references/rest-api">}}) and databases.
+
+## Set up certificate-based authentication
+
+To set up certificate-based authentication:
+
+1. [Add the `mtls_trusted_ca` certificate.](#add-cert) 
+
+1. [Configure cluster settings.](#config-cluster)
+
+1. If you want to enable certificate-based authentication for databases, you must [enable mutual TLS for the relevant databases](#enable-mtls-dbs). Otherwise, you can skip this step.
+
+1. [Create certificate auth_method users.](#create-cert-users)
+
+### Add mtls_trusted_ca certificate {#add-cert}
+
+Add a trusted CA certificate `mtls_trusted_ca` to the cluster using an [update cluster certificate]({{<relref "/operate/rs/references/rest-api/requests/cluster/certificates#put-cluster-update_cert">}}) request:
+
+```sh
+PUT /v1/cluster/update_cert
+{
+  "name": "mtls_trusted_ca",
+  "certificate": "<content of certificate PEM file>"
+}
+```
+
+### Configure cluster settings {#config-cluster}
+
+[Update cluster settings]({{<relref "/operate/rs/references/rest-api/requests/cluster#put-cluster">}}) with mutual TLS configuration.
+
+For certificate validation by Subject Alternative Name (SAN), use:
+
+```sh
+PUT /v1/cluster
+{
+  "mtls_certificate_authentication": true,
+  "mtls_client_cert_subject_validation_type": "san_cn",
+  "mtls_authorized_subjects": [{
+    "CN": "<Common Name>"
+  }]
+}
+```
+
+For certificate validation by full Subject Name, use:
+
+```sh
+PUT /v1/cluster
+{
+  "mtls_certificate_authentication": true,
+  "mtls_client_cert_subject_validation_type": "full_subject",
+  "mtls_authorized_subjects": [{
+    "CN": "<Common Name>",
+    "OU": [<array of Organizational Unit strings>],
+    "O": "<Organization>",
+    "C": "<2-letter country code>",
+    "L": "<Locality (city)>",
+    "ST": "<State/Province>"
+  }]
+}
+```
+
+Replace the placeholder values `<>` with your client certificate's subject values.
+
+### Enable mutual TLS for databases {#enable-mtls-dbs}
+
+Before you can connect to a database using certificate-based authentication, you must enable mutual TLS (mTLS). See [Enable TLS]({{<relref "/operate/rs/security/encryption/tls/enable-tls">}}) for detailed instructions.
+
+### Create certificate auth_method users {#create-cert-users}
+
+When you [create new users]({{<relref "/operate/rs/references/rest-api/requests/users#post-user">}}), include `"auth_method": "certificate"` and `certificate_subject_line` in the request body :
+
+```sh
+POST /v1/users
+{
+  "auth_method": "certificate",
+  "certificate_subject_line": "CN=<Common Name>, OU=<Organization Unit>, O=<Organization>, L=<Locality>, ST=<State/Province>, C=<Country>"
+}
+```
+
+Replace the placeholder values `<>` with your client certificate's subject values.
+
+## Authenticate REST API requests
+
+To use the REST API with certificate-based authentication, you must provide a client certificate, signed by the trusted CA `mtls_trusted_ca`, and a private key.
+
+The following example uses [cURL](https://curl.se/) to send a [REST API request]({{<relref "/operate/rs/references/rest-api/requests">}}):
+
+```sh
+curl --request <METHOD> --url https://<hostname-or-IP-address>:9443/<API-version>/<API-path> --cert client.pem --key client.key
+```
+
+## Authenticate database connections
+
+To connect to a database with certificate-based authentication, you must provide a client certificate, signed by the trusted CA `mtls_trusted_ca`, and a private key.
+
+The following example shows how to connect to a Redis database with [`redis-cli`]({{<relref "/operate/rs/references/cli-utilities/redis-cli">}}):
+
+```sh
+redis-cli -h <hostname-or-IP-address> -p <port> --tls --cacert <redis_cert>.pem --cert redis_user.crt --key redis_user_private.key
+```
+
+## Limitations
+
+- Certificate-based authentication is not implemented for the Cluster Manager UI.