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Integrate with Mattermost Team Edition

Support level: Community

What is Mattermost Team Edition​

Mattermost is an open source, real-time collaboration platform. It provides chat, audio/video calling, screen sharing, and a plugin architecture for extending its capabilities. Mattermost Team Edition is the free, open-source version of the product.

-- https://mattermost.com/

Preparation​

The following placeholders are used in this guide:

  • mattermost.company is the FQDN of the Mattermost installation.
  • authentik.company is the FQDN of the authentik installation.
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This documentation lists only the settings that you need to change from their default values. Be aware that any changes other than those explicitly mentioned in this guide could cause issues accessing your application.

Configuration methods​

You can configure Mattermost to use either OIDC or SAML, and this guide explains both options.

Mattermost OIDC support

Mattermost Team Edition does not natively support generic single sign-on. However, you can manually configure Mattermost to use its GitLab integration for authentication via authentik's OAuth2/OpenID Provider. This requires editing the config.json file directly, as the necessary settings are not available through the web interface. If you are using a hosted version of Mattermost without filesystem access, you will not be able to complete this setup.

Once configured, Mattermost will display a login button with the GitLab icon, but authentication will be handled entirely by authentik. GitLab itself is not required or used in any way.

authentik configuration​

To support the integration of Mattermost Team Edition with authentik, you need to create property mappings and an application/provider pair in authentik.

Create property mappings​

  1. Log in to authentik as an administrator and open the authentik Admin interface.
  2. Navigate to Customization > Property Mappings and click Create. Create a Scope Mapping with the following settings:
    • Name: mattermost-username
    • Scope Name: username
    • Description: Maps the user's authentik username to the username field for Mattermost authentication.
    • Expression: 
      return {
          "username": request.user.username,
      }
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The following id property mapping is optional. If omitted, Mattermost will generate user IDs based on email addresses, resulting in names such as person-example.com for person@example.com. Since these IDs serve as nicknames, this format may be undesirable.

  1. If desired, click Create again, and create another Scope Mapping with the following settings:
    • Name: mattermost-id
    • Scope Name: id
    • Description: Maps the user's Mattermost ID or primary key to the id field for Mattermost authentication.
    • Expression: 
      return {
          "id": request.user.attributes.get("mattermostId", request.user.pk),
      }

Create an application and provider in authentik​

  1. Log in to authentik as an administrator and open the authentik Admin interface.

  2. Navigate to Applications > Applications and click Create with Provider to create an application and provider pair. (Alternatively you can first create a provider separately, then create the application and connect it with the provider.)

    • Application: provide a descriptive name, an optional group for the type of application, and the policy engine mode. Take note of the Slug value because it will be required later.
    • Choose a Provider type: select OAuth2/OpenID Connect as the provider type.
    • Configure the Provider: provide a name (or accept the auto-provided name), the authorization flow to use for this provider, and the following required configurations.
      • Note the Client ID and Client Secret values because they will be required later.
      • Set a Strict redirect URI to https://mattermost.company/signup/gitlab/complete.
      • Select any available signing key.
      • Under Advanced protocol settings, add the scopes you just created to the list of selected scopes.
    • Configure Bindings (optional): you can create a binding (policy, group, or user) to manage the listing and access to applications on a user's My applications page.

  3. Click Submit to save the new application and provider.

Mattermost Team Edition configuration​

To support the integration of Mattermost Team Edition with authentik, you'll need to update the config.json file of your Mattermost deployment:

  1. Modify the GitLabSettings section to look like the following:
/opt/mattermost/config/config.json
"GitLabSettings": {
    "Enable": true,
    "Secret": "<client_secret>",
    "Id": "<client_id>",
    "Scope": "",
    "AuthEndpoint": "https://authentik.company/application/o/authorize/",
    "TokenEndpoint": "https://authentik.company/application/o/token/",
    "UserAPIEndpoint": "https://authentik.company/application/o/userinfo/",
    "DiscoveryEndpoint": "https://authentik.company/application/o/<application_slug>/.well-known/openid-configuration",
    "ButtonText": "Log in with authentik",
    "ButtonColor": "#000000"
},
  1. Log in to Mattermost as an administrator and navigate to the System Console. Go to Authentication > Signup options (https://mattermost.company/admin_console/authentication/signup) and make sure that Enable Account Creation is set to true.
  2. Restart Mattermost to apply the changes.

Configuration verification​

To verify the integration of authentik with Mattermost, log out and attempt to log back in. You should see a login button for authentik on the login page, and a successful login should redirect you to Mattermost without any errors.

Troubleshooting​

  • Missing email or username error: If logging in with SAML, ensure that any users logging into Mattermost from authentik have both an email address and username set in their authentik profile.

Resources​