# 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:

   ```shell
   sudo editor /etc/gitlab/gitlab.rb
   ```

   For installations from source:

   ```shell
   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:

   ```yaml
   - { 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. [Reconfigure](../administration/restart_gitlab.md#omnibus-gitlab-reconfigure) or
   [restart GitLab](../administration/restart_gitlab.md#installations-from-source) for the changes to
   take effect if you installed GitLab via Omnibus or from source respectively.

On the sign in page there should now be a CAS tab in the sign in form.
