Add Gitlab authentication

docs/github-authentication.markdown

@@ -11,7 +11,7 @@ How does this work?
 
 The Github authentication in Kanboard uses the [OAuth 2.0](http://oauth.net/2/) protocol, so any user of Kanboard can be linked to a Github account.
 
-That means you can use your Github account to connect to Kanboard.
+That means you can use your Github account to login on Kanboard.
 
 How to link a Github account
 ----------------------------

docs/gitlab-authentication.markdown

@@ -0,0 +1,78 @@
+Gitlab Authentication
+=====================
+
+Requirements
+------------
+
+- Account on [Gitlab.com](https://gitlab.com) or you own self-hosted Gitlab instance
+- Have Kanboard registered as application in Gitlab
+
+How does this work?
+-------------------
+
+The Gitlab authentication in Kanboard uses the [OAuth 2.0](http://oauth.net/2/) protocol, so any user of Kanboard can be linked to a Gitlab account.
+
+That means you can use your Gitlab account to login on Kanboard.
+
+How to link a Gitlab account
+----------------------------
+
+1. Go to your user profile
+2. Click on **External accounts**
+3. Click on the link **Link my Gitlab Account**
+4. You are redirected to the **Gitlab authorization form**
+5. Authorize Kanboard by clicking on the button **Accept**
+6. Your account is now linked
+
+Now, on the login page you can be authenticated in one click with the link **Login with my Gitlab Account**.
+
+Your name and email are automatically updated from your Gitlab Account if defined.
+
+Installation instructions
+-------------------------
+
+### Setting up OAuth 2.0
+
+- On Gitlab, register a new application by following the [official documentation](http://doc.gitlab.com/ce/integration/oauth_provider.html)
+- In Kanboard, you can get the **callback url** in **Settings > Integrations > Gitlab Authentication**, just copy and paste the url
+
+### Setting up Kanboard
+
+Either create a new `config.php` file or rename the `config.default.php` file and set the following values:
+
+```php
+// Enable/disable Gitlab authentication
+define('GITLAB_AUTH', true);
+
+// Gitlab application id
+define('GITLAB_CLIENT_ID', 'YOUR_APPLICATION_ID');
+
+// Gitlab application secret
+define('GITLAB_CLIENT_SECRET', 'YOUR_APPLICATION_SECRET');
+```
+
+### Custom endpoints for self-hosted Gitlab
+
+Change these default values if you use a self-hosted instance of Gitlab:
+
+```php
+// Gitlab oauth2 authorize url
+define('GITLAB_OAUTH_AUTHORIZE_URL', 'https://gitlab.com/oauth/authorize');
+
+// Gitlab oauth2 token url
+define('GITLAB_OAUTH_TOKEN_URL', 'https://gitlab.com/oauth/token');
+
+// Gitlab API url endpoint (don't forget the slash at the end)
+define('GITLAB_API_URL', 'https://gitlab.com/api/v3/');
+```
+
+Notes
+-----
+
+Kanboard uses these information from your Gitlab profile:
+
+- Full name
+- Email address
+- Gitlab unique id
+
+The Gitlab unique id is used to link the local user account and the Gitlab account.

docs/index.markdown

@@ -122,6 +122,7 @@ Technical details
 - [LDAP authentication](ldap-authentication.markdown)
 - [Google authentication](google-authentication.markdown)
 - [Github authentication](github-authentication.markdown)
+- [Gitlab authentication](gitlab-authentication.markdown)
 - [Reverse proxy authentication](reverse-proxy-authentication.markdown)
 
 ### Contributors