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+# CAS OmniAuth Provider
+
+To enable the CAS OmniAuth provider you must register your application with your CAS instance. This requires the service URL GitLab will supply to CAS. It should be something like: `https://gitlab.example.com:443/users/auth/cas3/callback?url`. By default handling for SLO is enabled, you only need to configure CAS for backchannel logout.
+
+1.  On your GitLab server, open the configuration file.
+
+    For omnibus package:
+
+    ```sh
+      sudo editor /etc/gitlab/gitlab.rb
+    ```
+
+    For installations from source:
+
+    ```sh
+      cd /home/git/gitlab
+
+      sudo -u git -H editor config/gitlab.yml
+    ```
+
+1.  See [Initial OmniAuth Configuration](omniauth.md#initial-omniauth-configuration) for initial settings.
+
+1.  Add the provider configuration:
+
+    For omnibus package:
+
+    ```ruby
+      gitlab_rails['omniauth_providers'] = [
+        {
+          name: "cas3",
+          label: "cas",
+          args: {
+                  url: 'CAS_SERVER',
+                  login_url: '/CAS_PATH/login',
+                  service_validate_url: '/CAS_PATH/p3/serviceValidate',
+                  logout_url: '/CAS_PATH/logout'} }
+          }
+        }
+      ]
+    ```
+
+    For installations from source:
+
+    ```
+      - { name: 'cas3',
+          label: 'cas',
+          args: {
+                  url: 'CAS_SERVER',
+                  login_url: '/CAS_PATH/login',
+                  service_validate_url: '/CAS_PATH/p3/serviceValidate',
+                  logout_url: '/CAS_PATH/logout'} }
+    ```
+
+1.  Change 'CAS_PATH' to the root of your CAS instance (ie. `cas`).
+
+1.  If your CAS instance does not use default TGC lifetimes, update the `cas3.session_duration` to at least the current TGC maximum lifetime. To explicitly disable SLO, regardless of CAS settings, set this to 0.
+
+1.  Save the configuration file.
+
+1.  Restart GitLab for the changes to take effect.
+
+On the sign in page there should now be a CAS tab in the sign in form.