feat: Docs for client secret rotation

docs/hydra/guides/oauth2-clients.mdx

@@ -180,6 +180,144 @@ See [API documentation](../../reference/api#tag/oAuth2/operation/patchOAuth2Clie
 </Tabs>
 ````
 
+## Rotate OAuth2 client secret
+
+OAuth2 client secret rotation allows you to change a client's secret without downtime. When you rotate a secret, the old secret
+remains valid until you remove it, allowing you to update all your client services without service interruption.
+
+##### How secret rotation works
+
+1. Generate a new secret for the client service. Both the old and the new secrets can be used to authenticate from this point on.
+2. Update your client services to use the new secret.
+3. Test that the client services can authenticate with the new secret.
+4. Manually remove the old secret. Only the new secret authenticates from this point on.
+
+:::info
+
+Secret rotation is available only for clients that use the `client_secret_basic` or `client_secret_post` token endpoint
+authentication method. Ory keeps up to five rotated secrets per client. When you rotate again, the oldest rotated secret is
+dropped and can no longer authenticate. Setting a new secret through the update or patch client APIs clears all rotated secrets.
+
+:::
+
+##### Rotate OAuth2 client secret
+
+To rotate an OAuth2 client secret, use the following methods:
+
+````mdx-code-block
+<Tabs>
+<TabItem value="rest" label="REST API">
+
+```bash
+curl -X POST https://{project.slug}.projects.oryapis.com/admin/clients/{client-id}/secrets/rotate \
+  -H "Authorization: Bearer ory_pat_..."
+```
+
+The response includes the new `client_secret`. Ory shows this value only once. Store it immediately in the secret store that your
+client services read from, such as a secrets manager or an encrypted environment configuration.
+
+See [API documentation](../../reference/api#tag/oAuth2/operation/rotateOAuth2ClientSecret).
+
+</TabItem>
+<TabItem value="sdk" label="Ory SDK">
+
+```typescript
+import { Configuration, OAuth2Api } from "@ory/client"
+
+const ory = new OAuth2Api(
+  new Configuration({
+    basePath: `https://${projectSlug}.projects.oryapis.com`,
+    accessToken: "ory_pat_..."
+  })
+)
+
+const { data: client } = await ory.rotateOAuth2ClientSecret({
+  id: clientId
+})
+
+// Save the new client_secret immediately
+console.log("New secret:", client.client_secret)
+```
+
+</TabItem>
+</Tabs>
+````
+
+##### Remove old secret
+
+Once all services are updated to use the new secret, remove the old secret to revoke access using the old secret:
+
+````mdx-code-block
+<Tabs>
+<TabItem value="rest" label="REST API">
+
+```bash
+curl -X DELETE https://{project.slug}.projects.oryapis.com/admin/clients/{client-id}/secrets/rotate \
+  -H "Authorization: Bearer ory_pat_..."
+```
+
+After removing the old secret, only the current (new) secret is valid. The old secret can no longer authenticate.
+
+See [API documentation](../../reference/api#tag/oAuth2/operation/deleteRotatedOAuth2ClientSecrets).
+
+</TabItem>
+<TabItem value="sdk" label="Ory SDK">
+
+```typescript
+await ory.deleteRotatedOAuth2ClientSecrets({
+  id: clientId
+})
+
+// Old secret is now revoked.
+```
+
+</TabItem>
+</Tabs>
+````
+
+##### Secret rotation workflow example
+
+Here's a complete workflow for rotating a client secret:
+
+```bash
+# 1. Get current client
+CLIENT_ID="your-client-id"
+
+# 2. Rotate the secret
+NEW_SECRET=$(curl -X POST "https://{project.slug}.projects.oryapis.com/admin/clients/$CLIENT_ID/secrets/rotate" \
+  -H "Authorization: Bearer ory_pat_..." | jq -r '.client_secret')
+
+echo "New secret: $NEW_SECRET"
+
+# 3. Update your client services with the new secret
+# (Both the old and the new secrets work during this period)
+
+# 4. Verify the new secret works
+curl -X POST "https://{project.slug}.projects.oryapis.com/oauth2/token" \
+  -u "$CLIENT_ID:$NEW_SECRET" \
+  -d "grant_type=client_credentials"
+
+# 5. Once all client services are updated, remove the old secret
+curl -X DELETE "https://{project.slug}.projects.oryapis.com/admin/clients/$CLIENT_ID/secrets/rotate" \
+  -H "Authorization: Bearer ory_pat_..."
+
+# Old secret is now revoked
+```
+
+:::tip Zero-downtime credential rotation
+
+Secret rotation enables zero-downtime credential updates. Both the old and new secrets remain valid until you remove the
+old secret, allowing you to update all your client services without service interruption.
+
+:::
+
+:::warning Security best practice
+
+Secrets remain valid indefinitely until you explicitly remove them. Always remove old secrets once your secret rotation process is
+complete to ensure that compromised credentials cannot be used.
+
+:::
+
 ## Delete OAuth2 client
 
 To delete an existing OAuth2 client, use the following methods: