GitLab Single Sign-On 

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Configuring GitLab as a Single Sign-On (SSO) service 

Follow these steps to configure Mattermost to use GitLab as a Single Sign-on (SSO) service for team creation, account creation, and user login.

Note

  • Only the default GitLab SSO is officially supported.

  • “Double SSO”, where GitLab SSO is chained to other SSO solutions, is not supported. It may be possible to connect GitLab SSO with AD, LDAP, SAML, or MFA add-ons in some cases, but because of the special logic required, they’re not officially supported, and they’re known not to work in some cases.

  • Mattermost’s open source Team Edition supports the OAuth 2.0 standard.

  • Mattermost Professional and Enterprise support the OpenID Connect standard.

Step 1: Add an OpenID Connect application to your GitLab account 

  1. Log in to your GitLab account, then go to https://{gitlab-site-name}/profile/applications. For {gitlab-site-name} use the name of your GitLab instance. If you’re using GitLab itself as your service provider, use gitlab.com.

  2. Add a new application:

  1. In the Name field, enter Mattermost.

  2. In the Redirect URI field, add the following two lines using your own value for {mattermost-site-name}.

https://{mattermost-site-name}/login/gitlab/complete
https://{mattermost-site-name}/signup/gitlab/complete

If your GitLab instance is not set up to use SSL, your URIs must begin with http:// instead of https://.

  1. Select scopes.

    • For Mattermost Team Edition, select read_user.

    • For Mattermost Enterprise, select openid, profile, and email.

  1. Select Save application.

  2. Keep the GitLab window open. You need the Application Id and Application Secret Key when you configure Mattermost.

Step 2: Configure Mattermost for GitLab SSO 

  1. Log in to Mattermost, then go to System Console > Authentication > OpenID Connect.

  2. Select GitLab as the service provider.

  3. Enter the Gitlab Site URL of your GitLab instance. If your GitLab instance is not set up to use SSL, start the URL with http:// instead of https://. If you are using GitLab itself as your provider, use gitlab.com.

  4. The Discovery Endpoint for OpenID Connect with GitLab is prepopulated with https://gitlab.com/.well-known/openid-configuration.

  5. Paste the Application ID from GitLab as the Client ID in Mattermost.

  6. Paste the Application Secret Key from GitLab as the Client Secret in Mattermost.

  7. Update the config.json file and specify the scopes you selected in GitLab under the GitLabSettings property. At a minimum, openid is a required scope for Mattermost Professional and Enterprise, and read_user is a required scope for Mattermost Team Edition. Changes to this setting require a server restart before taking effect.

  8. Select Save.

Note

  • When Mattermost is configured to use OpenID Connect or OAuth 2.0 for user authentication, the following user attribute changes can’t be made through the Mattermost API: first name, last name, or username. OpenID Connect or OAuth 2.0 must be the authoritative source for these user attributes.

  • If you are using Mattermost behind a load balancer and you have SSL configured, you may need to set X-Forwarded-Proto header to https at your load balancer.

(Optional) Step 3: Force users to sign up using SSO only 

To force all users to sign-up with SSO only, set System Console > Authentication > Email > Enable sign-in with email to false Users must change their login method before they can log in to Mattermost with GitLab.

Frequently Asked Questions 

How can I use LDAP attributes or Groups with OpenID? 

At this time, LDAP data isn’t compatible with OpenID. If you currently rely on LDAP to manage your users’ teams, channels, groups, or attributes, you won’t be able to do this automatically with users who have logged in with OpenID. If you need LDAP synced to each user, we suggest using SAML or LDAP as the login provider. Some OpenID providers can use SAML instead, like Keycloak.