OpenID Connect OmniAuth provider

GitLab can use OpenID Connect as an OmniAuth provider.

To enable the OpenID Connect OmniAuth provider, you must register your application with an OpenID Connect provider. The OpenID Connect provides you with a client’s details and secret for you to use.

On your GitLab server, open the configuration file.
For Omnibus GitLab:
```
sudo editor /etc/gitlab/gitlab.rb
```
For installations from source:
```
cd /home/git/gitlab
sudo -u git -H editor config/gitlab.yml
```
See Initial OmniAuth Configuration for initial settings.

Add the provider configuration.

For Omnibus GitLab:

gitlab_rails['omniauth_providers'] = [
  { 'name' => 'openid_connect',
    'label' => '<your_oidc_label>',
    'icon' => '<custom_provider_icon>',
    'args' => {
      'name' => 'openid_connect',
      'scope' => ['openid','profile'],
      'response_type' => 'code',
      'issuer' => '<your_oidc_url>',
      'discovery' => true,
      'client_auth_method' => 'query',
      'uid_field' => '<uid_field>',
      'send_scope_to_token_endpoint' => 'false',
      'client_options' => {
        'identifier' => '<your_oidc_client_id>',
        'secret' => '<your_oidc_client_secret>',
        'redirect_uri' => '<your_gitlab_url>/users/auth/openid_connect/callback'
      }
    }
  }
]

For installation from source:

  - { name: 'openid_connect',
      label: '<your_oidc_label>',
      icon: '<custom_provider_icon>',
      args: {
        name: 'openid_connect',
        scope: ['openid','profile'],
        response_type: 'code',
        issuer: '<your_oidc_url>',
        discovery: true,
        client_auth_method: 'query',
        uid_field: '<uid_field>',
        send_scope_to_token_endpoint: false,
        client_options: {
          identifier: '<your_oidc_client_id>',
          secret: '<your_oidc_client_secret>',
          redirect_uri: '<your_gitlab_url>/users/auth/openid_connect/callback'
        }
      }
    }

For more information on each configuration option refer to the OmniAuth OpenID Connect usage documentation and the OpenID Connect Core 1.0 specification.

For the configuration above, change the values for the provider to match your OpenID Connect client setup. Use the following as a guide:
- <your_oidc_label> is the label that appears on the login page.
- <custom_provider_icon> (optional) is the icon that appears on the login page. Icons for the major social login platforms are built-in into GitLab, but can be overridden by specifying this parameter. Both local paths and absolute URLs are accepted.
- <your_oidc_url> (optional) is the URL that points to the OpenID Connect provider. For example, https://example.com/auth/realms/your-realm. If this value is not provided, the URL is constructed from the client_options in the following format: <client_options.scheme>://<client_options.host>:<client_options.port>.
- If discovery is set to true, the OpenID Connect provider attempts to auto discover the client options using <your_oidc_url>/.well-known/openid-configuration. Defaults to false.
- client_auth_method (optional) specifies the method used for authenticating the client with the OpenID Connect provider.
  - Supported values are:
    - basic - HTTP Basic Authentication
    - jwt_bearer - JWT based authentication (private key and client secret signing)
    - mtls - Mutual TLS or X.509 certificate validation
    - Any other value POSTs the client ID and secret in the request body
  - If not specified, defaults to basic.
- <uid_field> (optional) is the field name from the user_info.raw_attributes that defines the value for uid. For example, preferred_username. If this value is not provided or the field with the configured value is missing from the user_info.raw_attributes details, the uid uses the sub field.
- send_scope_to_token_endpoint is true by default. In other words, the scope parameter is normally included in requests to the token endpoint. However, if your OpenID Connect provider does not accept the scope parameter in such requests, set this to false.
- client_options are the OpenID Connect client-specific options. Specifically:
  - identifier is the client identifier as configured in the OpenID Connect service provider.
  - secret is the client secret as configured in the OpenID Connect service provider.
  - redirect_uri is the GitLab URL to redirect the user to after successful login. For example, http://example.com/users/auth/openid_connect/callback.
  - end_session_endpoint (optional) is the URL to the endpoint that end the session (logout). Can be provided if auto-discovery disabled or unsuccessful.
  - The following client_options are optional unless auto-discovery is disabled or unsuccessful:
    - authorization_endpoint is the URL to the endpoint that authorizes the end user.
    - token_endpoint is the URL to the endpoint that provides Access Token.
    - userinfo_endpoint is the URL to the endpoint that provides the user information.
    - jwks_uri is the URL to the endpoint where the Token signer publishes its keys.
Save the configuration file.
Reconfigure or restart GitLab 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 an OpenID Connect icon below the regular sign in form. Click the icon to begin the authentication process. The OpenID Connect provider asks the user to sign in and authorize the GitLab application (if confirmation required by the client). If everything goes well, the user is redirected to GitLab and signed in.

Example configurations

The following configurations illustrate how to set up OpenID with different providers with Omnibus GitLab.

Google

See the Google documentation for more details:

gitlab_rails['omniauth_providers'] = [
  {
    'name' => 'openid_connect',
    'label' => 'Google OpenID',
    'args' => {
      'name' => 'openid_connect',
      'scope' => ['openid', 'profile', 'email'],
      'response_type' => 'code',
      'issuer' => 'https://accounts.google.com',
      'client_auth_method' => 'query',
      'discovery' => true,
      'uid_field' => 'preferred_username',
      'client_options' => {
        'identifier' => '<YOUR PROJECT CLIENT ID>',
        'secret' => '<YOUR PROJECT CLIENT SECRET>',
        'redirect_uri' => 'https://example.com/users/auth/openid_connect/callback',
       }
     }
  }
]

Microsoft Azure

The OpenID Connect (OIDC) protocol for Microsoft Azure uses the Microsoft identity platform (v2) endpoints. To get started, sign in to the Azure Portal. For your app, you’ll need the following information:

A tenant ID. You may already have one. For more information, review the Microsoft Azure Tenant documentation.
A client ID and a client secret. Follow the instructions in the Microsoft Quickstart Register an Application documentation. to obtain the tenant ID, client ID, and client secret for your app.

Example Omnibus configuration block:

gitlab_rails['omniauth_providers'] = [
  {
    'name' => 'openid_connect',
    'label' => 'Azure OIDC',
    'args' => {
      'name' => 'openid_connect',
      'scope' => ['openid', 'profile', 'email'],
      'response_type' => 'code',
      'issuer' =>  'https://login.microsoftonline.com/<YOUR-TENANT-ID>/v2.0',
      'client_auth_method' => 'query',
      'discovery' => true,
      'uid_field' => 'preferred_username',
      'client_options' => {
        'identifier' => '<YOUR APP CLIENT ID>',
        'secret' => '<YOUR APP CLIENT SECRET>',
        'redirect_uri' => 'https://gitlab.example.com/users/auth/openid_connect/callback'
      }
    }
  }
]

Microsoft has documented how its platform works with the OIDC protocol.

Microsoft Azure Active Directory B2C

While GitLab works with Azure Active Directory B2C, it requires special configuration to work. To get started, sign in to the Azure Portal. For your app, you’ll need the following information from Azure:

A tenant ID. You may already have one. For more information, review the Microsoft Azure Tenant documentation.
A client ID and a client secret. Follow the instructions in the Microsoft tutorial documentation to obtain the client ID and client secret for your app.
The user flow or policy name. Follow the instructions in the Microsoft tutorial.

If your GitLab domain is gitlab.example.com, ensure the app has the following Redirect URI:

https://gitlab.example.com/users/auth/openid_connect/callback

In addition, ensure that ID tokens are enabled.

Add the following API permissions to the app:

openid
offline_access

Configure custom policies

Azure B2C offers two ways of defining the business logic for logging in a user:

While cumbersome to configure, custom policies are required because standard Azure B2C user flows do not send the OpenID email claim. In other words, they do not work with the allow_single_sign_on or auto_link_user parameters. With a standard Azure B2C policy, GitLab cannot create a new account or link to an existing one with an e-mail address.

Carefully follow the instructions for creating a custom policy.

The Microsoft instructions use SocialAndLocalAccounts in the custom policy starter pack, but LocalAccounts works for authenticating against local, Active Directory accounts. Before you follow the instructions to upload the polices, do the following:

To export the email claim, modify the SignUpOrSignin.xml. Replace the following line:

 <OutputClaim ClaimTypeReferenceId="email" />

with:

 <OutputClaim ClaimTypeReferenceId="signInNames.emailAddress" PartnerClaimType="email" />

For OIDC discovery to work with B2C, the policy must be configured with an issuer compatible with the OIDC specification. See the token compatibility settings. In TrustFrameworkBase.xml under JwtIssuer, set IssuanceClaimPattern to AuthorityWithTfp:

 <ClaimsProvider>
   <DisplayName>Token Issuer</DisplayName>
   <TechnicalProfiles>
     <TechnicalProfile Id="JwtIssuer">
       <DisplayName>JWT Issuer</DisplayName>
       <Protocol Name="None" />
       <OutputTokenFormat>JWT</OutputTokenFormat>
       <Metadata>
         <Item Key="IssuanceClaimPattern">AuthorityWithTfp</Item>
         ...

Now upload the policy. Overwrite the existing files if you are updating an existing policy.
Determine the issuer URL using the sign-in policy. The issuer URL will be in the form:
```
 https://<YOUR-DOMAIN>/tfp/<YOUR-TENANT-ID>/<YOUR-SIGN-IN-POLICY-NAME>/v2.0/
```
The policy name is lowercased in the URL. For example, B2C_1A_signup_signin policy appears as b2c_1a_signup_sigin.
Note that the trailing forward slash is required.

Verify the operation of the OIDC discovery URL and issuer URL, append .well-known/openid-configuration to the issuer URL:

 https://<YOUR-DOMAIN>/tfp/<YOUR-TENANT-ID>/<YOUR-SIGN-IN-POLICY-NAME>/v2.0/.well-known/openid-configuration

For example, if domain is example.b2clogin.com and tenant ID is fc40c736-476c-4da1-b489-ee48cee84386, you can use curl and jq to extract the issuer:

 $ curl --silent "https://example.b2clogin.com/tfp/fc40c736-476c-4da1-b489-ee48cee84386/b2c_1a_signup_signin/v2.0/.well-known/openid-configuration" | jq .issuer
 "https://example.b2clogin.com/tfp/fc40c736-476c-4da1-b489-ee48cee84386/b2c_1a_signup_signin/v2.0/"

Configure the issuer URL with the custom policy used for signup_signin. For example, this is the Omnibus configuration with a custom policy for b2c_1a_signup_signin:

gitlab_rails['omniauth_providers'] = [
{
  'name' => 'openid_connect',
  'label' => 'Azure B2C OIDC',
  'args' => {
    'name' => 'openid_connect',
    'scope' => ['openid'],
    'response_mode' => 'query',
    'response_type' => 'id_token',
    'issuer' =>  'https://<YOUR-DOMAIN>/tfp/<YOUR-TENANT-ID>/b2c_1a_signup_signin/v2.0/',
    'client_auth_method' => 'query',
    'discovery' => true,
    'send_scope_to_token_endpoint' => true,
    'client_options' => {
      'identifier' => '<YOUR APP CLIENT ID>',
      'secret' => '<YOUR APP CLIENT SECRET>',
      'redirect_uri' => 'https://gitlab.example.com/users/auth/openid_connect/callback'
    }
  }
}]

Troubleshooting Azure B2C

Ensure all occurrences of yourtenant.onmicrosoft.com, ProxyIdentityExperienceFrameworkAppId, and IdentityExperienceFrameworkAppId match your B2C tenant hostname and the respective client IDs in the XML policy files.
Add https://jwt.ms as a redirect URI to the app, and use the custom policy tester. Make sure the payload includes email that matches the user’s e-mail access.
After you enable the custom policy, users might see “Invalid username or password” after they try to sign in. This might be a configuration issue with the IdentityExperienceFramework app. See this Microsoft comment that suggests checking that the app manifest contains these settings:
- "accessTokenAcceptedVersion": null
- "signInAudience": "AzureADMyOrg"
  Note that this configuration corresponds with the Supported account types setting used when creating the IdentityExperienceFramework app.

General troubleshooting

If you’re having trouble, here are some tips:

Ensure discovery is set to true. Setting it to false requires specifying all the URLs and keys required to make OpenID work.
Check your system clock to ensure the time is synchronized properly.
As mentioned in the documentation, make sure issuer corresponds to the base URL of the Discovery URL. For example, https://accounts.google.com is used for the URL https://accounts.google.com/.well-known/openid-configuration.
The OpenID Connect client uses HTTP Basic Authentication to send the OAuth2 access token if client_auth_method is not defined or if set to basic. If you are seeing 401 errors upon retrieving the userinfo endpoint, you may want to check your OpenID Web server configuration. For example, for oauth2-server-php, you may need to add a configuration parameter to Apache.