OpenID Connect OmniAuth provider (FREE SELF)

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.

1. 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

2. Configure the common settings to add openid_connect as a single sign-on provider. This enables Just-In-Time account provisioning for users who do not have an existing GitLab account.

3. Add the provider configuration.

   For Omnibus GitLab:

   gitlab_rails['omniauth_providers'] = [
     {
       name: "openid_connect", # do not change this parameter
       label: "Provider name", # optional label for login button, defaults to "Openid Connect"
       icon: "<custom_provider_icon>",
       args: {
         name: "openid_connect",
         scope: ["openid","profile","email"],
         response_type: "code",
         issuer: "<your_oidc_url>",
         discovery: true,
         client_auth_method: "query",
         uid_field: "<uid_field>",
         send_scope_to_token_endpoint: "false",
         pkce: true,
         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', # do not change this parameter
         label: 'Provider name', # optional label for login button, defaults to "Openid Connect"
         icon: '<custom_provider_icon>',
         args: {
           name: 'openid_connect',
           scope: ['openid','profile','email'],
           response_type: 'code',
           issuer: '<your_oidc_url>',
           discovery: true,
           client_auth_method: 'query',
           uid_field: '<uid_field>',
           send_scope_to_token_endpoint: false,
           pkce: true,
           client_options: {
             identifier: '<your_oidc_client_id>',
             secret: '<your_oidc_client_secret>',
             redirect_uri: '<your_gitlab_url>/users/auth/openid_connect/callback'
           }
         }
       }

   NOTE: For more information on each configuration option, refer to the:

   • OmniAuth OpenID Connect usage documentation.
   • OpenID Connect Core 1.0 specification.

4. For the provider configuration, 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 into GitLab, but you can override these icons by specifying this parameter. GitLab accepts both local paths and absolute URLs.
   • <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 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 automatically 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, this value defaults to basic.
   • <uid_field> (optional) is the field name from user_info.raw_attributes that defines the value for uid (for example, preferred_username). If you do not provide this value, or the field with the configured value is missing from the user_info.raw_attributes details, uid uses the sub field.
   • send_scope_to_token_endpoint is true by default, so the scope parameter is usually 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.
   • pkce (optional): Enable Proof Key for Code Exchange. Available in GitLab 15.9.
   • 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. For example, OmniAuth OpenIDConnect) requires this. If the service provider doesn't require a secret, provide any value and it is ignored.
     • 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 ends the session. You can provide this URL if auto-discovery is 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.

5. Save the configuration file.

6. For changes to take effect, if you installed GitLab:

   • With Omnibus, reconfigure GitLab.
   • From source, restart GitLab.

On the sign in page, you have an OpenID Connect option below the regular sign in form. Select this option to begin the authentication process. The OpenID Connect provider asks you to sign in and authorize the GitLab application if confirmation is required by the client. You are redirected to GitLab and signed in.

Example configurations

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

Configure Google

See the Google documentation for more details:

gitlab_rails['omniauth_providers'] = [
  {
    name: "openid_connect", # do not change this parameter
    label: "Google OpenID", # optional label for login button, defaults to "Openid Connect"
    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",
      pkce: true,
      client_options: {
        identifier: "<YOUR PROJECT CLIENT ID>",
        secret: "<YOUR PROJECT CLIENT SECRET>",
        redirect_uri: "https://example.com/users/auth/openid_connect/callback",
       }
     }
  }
]

Configure 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 need the following information:

• A tenant ID. You may already have one. For more information, see 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", # do not change this parameter
    label: "Azure OIDC", # optional label for login button, defaults to "Openid Connect"
    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",
      pkce: true,
      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.

Configure Microsoft Azure Active Directory B2C

GitLab requires special configuration to work with Azure Active Directory B2C. To get started, sign in to the Azure Portal. For your app, you 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.

Configure the app:

1. Set the app Redirect URI. For example, If your GitLab domain is gitlab.example.com, set the app Redirect URI to https://gitlab.example.com/users/auth/openid_connect/callback.

2. Enable the ID tokens.

3. 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:

• User flows
• Custom policies

Custom policies are required because standard Azure B2C user flows do not send the OpenID email claim. Therefore, the standard user flows 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 account with an email address.

First, create a custom policy.

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

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

   <OutputClaim ClaimTypeReferenceId="email" />

   with:

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

2. For OIDC discovery to work with B2C, configure the policy 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>
           ...

3. Upload the policy. Overwrite the existing files if you are updating an existing policy.

4. To determine the issuer URL, use the sign-in policy. The issuer URL is in the form:

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

   The policy name is lowercase in the URL. For example, B2C_1A_signup_signin policy appears as b2c_1a_signup_sigin.

   Ensure you include the trailing forward slash.

5. Verify the operation of the OIDC discovery URL and issuer URL and 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/"

6. 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", # do not change this parameter
     label: "Azure B2C OIDC", # optional label for login button, defaults to "Openid Connect"
     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,
       pkce: 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. Ensure the payload includes email that matches the user's email 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 you check that the app manifest contains these settings:

  • "accessTokenAcceptedVersion": null
  • "signInAudience": "AzureADMyOrg"

This configuration corresponds with the Supported account types setting used when creating the IdentityExperienceFramework app.

Configure Keycloak

GitLab works with OpenID providers that use HTTPS. Although you can set up a Keycloak server that uses HTTP, GitLab can only communicate with a Keycloak server that uses HTTPS.

Configure Keycloak to use public key encryption algorithms (for example, RSA256 or RSA512) instead of symmetric key encryption algorithms (for example, HS256 or HS358) to sign tokens. Public key encryption algorithms are:

• Easier to configure.
• More secure because leaking the private key has severe security consequences.

1. Open the Keycloak administration console.
2. Select Realm Settings > Tokens > Default Signature Algorithm.
3. Configure the signature algorithm.

Example Omnibus configuration block:

gitlab_rails['omniauth_providers'] = [
  {
    name: "openid_connect", # do not change this parameter
    label: "Keycloak", # optional label for login button, defaults to "Openid Connect"
    args: {
      name: "openid_connect",
      scope: ["openid", "profile", "email"],
      response_type: "code",
      issuer:  "https://keycloak.example.com/realms/myrealm",
      client_auth_method: "query",
      discovery: true,
      uid_field: "preferred_username",
      pkce: true,
      client_options: {
        identifier: "<YOUR CLIENT ID>",
        secret: "<YOUR CLIENT SECRET>",
        redirect_uri: "https://gitlab.example.com/users/auth/openid_connect/callback"
      }
    }
  }
]

Configure Keycloak with a symmetric key algorithm

Introduced in GitLab 14.2.

WARNING: The following instructions are included for completeness, but only use symmetric key encryption if absolutely necessary.

To use symmetric key encryption:

1. Extract the secret key from the Keycloak database. Keycloak does not expose this value in the web interface. The client secret seen in the web interface is the OAuth 2.0 client secret, which is different from the secret used to sign JSON Web Tokens.

   For example, if you use PostgreSQL as the backend database for Keycloak:

   • Sign into the database console.

   • Run the following SQL query to extract the key:

     $ psql -U keycloak
     psql (13.3 (Debian 13.3-1.pgdg100+1))
     Type "help" for help.
     
     keycloak=# SELECT c.name, value FROM component_config CC INNER JOIN component C ON(CC.component_id = C.id) WHERE C.realm_id = 'master' and provider_id = 'hmac-generated' AND CC.name = 'secret';
     -[ RECORD 1 ]---------------------------------------------------------------------------------
     name  | hmac-generated
     value | lo6cqjD6Ika8pk7qc3fpFx9ysrhf7E62-sqGc8drp3XW-wr93zru8PFsQokHZZuJJbaUXvmiOftCZM3C4KW3-g
     -[ RECORD 2 ]---------------------------------------------------------------------------------
     name  | fallback-HS384
     value | UfVqmIs--U61UYsRH-NYBH3_mlluLONpg_zN7CXEwkJcO9xdRNlzZfmfDLPtf2xSTMvqu08R2VhLr-8G-oZ47A

     In this example, there are two private keys: one for HS256 (hmac-generated) and another for HS384 (fallback-HS384). We use the first value to configure GitLab.

2. Convert value to standard base64. As discussed in the Invalid signature with HS256 token post, value is encoded in the Base 64 Encoding with URL and Filename Safe Alphabet section of RFC 4648. This must be converted to standard base64 as defined in RFC 2045. The following Ruby script does this:

   require 'base64'
   
   value = "lo6cqjD6Ika8pk7qc3fpFx9ysrhf7E62-sqGc8drp3XW-wr93zru8PFsQokHZZuJJbaUXvmiOftCZM3C4KW3-g"
   Base64.encode64(Base64.urlsafe_decode64(value))

   This results in the following value:

   lo6cqjD6Ika8pk7qc3fpFx9ysrhf7E62+sqGc8drp3XW+wr93zru8PFsQokH\nZZuJJbaUXvmiOftCZM3C4KW3+g==\n

3. Specify this base64-encoded secret in jwt_secret_base64. For example:

   gitlab_rails['omniauth_providers'] = [
     {
       name: "openid_connect", # do not change this parameter
       label: "Keycloak", # optional label for login button, defaults to "Openid Connect"
       args: {
         name: "openid_connect",
         scope: ["openid", "profile", "email"],
         response_type: "code",
         issuer:  "https://keycloak.example.com/auth/realms/myrealm",
         client_auth_method: "query",
         discovery: true,
         uid_field: "preferred_username",
         jwt_secret_base64: "<YOUR BASE64-ENCODED SECRET>",
         pkce: true,
         client_options: {
           identifier: "<YOUR CLIENT ID>",
           secret: "<YOUR CLIENT SECRET>",
           redirect_uri: "https://gitlab.example.com/users/auth/openid_connect/callback"
         }
       }
     }
   ]

If you see a JSON::JWS::VerificationFailed error, you have specified the wrong secret.

Casdoor

GitLab works with OpenID providers that use HTTPS. Use HTTPS to connect to GitLab through OpenID with Casdoor.

For your app, complete the following steps on Casdoor:

1. Get a client ID and a client secret.
2. Add your GitLab redirect URL. For example, if your GitLab domain is gitlab.example.com, ensure the Casdoor app has the following Redirect URI: https://gitlab.example.com/users/auth/openid_connect/callback.

See the Casdoor documentation for more details.

Example Omnibus GitLab configuration (file path: /etc/gitlab/gitlab.rb):

gitlab_rails['omniauth_providers'] = [
    {
        name: "openid_connect", # do not change this parameter
        label: "Casdoor", # optional label for login button, defaults to "Openid Connect"
        args: {
            name: "openid_connect",
            scope: ["openid", "profile", "email"],
            response_type: "code",
            issuer:  "https://<CASDOOR_HOSTNAME>",
            client_auth_method: "query",
            discovery: true,
            uid_field: "sub",
            client_options: {
                identifier: "<YOUR CLIENT ID>",
                secret: "<YOUR CLIENT SECRET>",
                redirect_uri: "https://gitlab.example.com/users/auth/openid_connect/callback"
            }
        }
    }
]

Example installations from source configuration (file path: config/gitlab.yml):

  - { name: 'openid_connect', # do not change this parameter
      label: 'Casdoor', # optional label for login button, defaults to "Openid Connect"
      args: {
        name: 'openid_connect',
        scope: ['openid','profile','email'],
        response_type: 'code',
        issuer: 'https://<CASDOOR_HOSTNAME>',
        discovery: true,
        client_auth_method: 'query',
        uid_field: 'sub',
        client_options: {
          identifier: '<YOUR CLIENT ID>',
          secret: '<YOUR CLIENT SECRET>',
          redirect_uri: 'https://gitlab.example.com/users/auth/openid_connect/callback'
        }
      }
    }

Configure users based on OIDC group membership (PREMIUM)

Introduced in GitLab 15.10.

You can configure OIDC group membership to:

• Require users to be members of a certain group.
• Assign users external roles, or as administrators based on group membership.

GitLab checks these groups on each sign in and updates user attributes as necessary. This feature does not allow you to automatically add users to GitLab groups.

Required groups

Your identity provider (IdP) must pass group information to GitLab in the OIDC response. To use this response to require users to be members of a certain group, configure GitLab to identify:

• Where to look for the groups in the OIDC response, using the groups_attribute setting.
• Which group membership is required to sign in, using the required_groups setting.

If you do not set required_groups or leave the setting empty, any user authenticated by the IdP through OIDC can use GitLab.

For Omnibus GitLab:

1. Edit /etc/gitlab/gitlab.rb:

   gitlab_rails['omniauth_providers'] = [
     {
       name: "openid_connect",
       label: "Provider name",
       args: {
         name: "openid_connect",
         scope: ["openid","profile","email"],
         response_type: "code",
         issuer: "<your_oidc_url>",
         discovery: true,
         client_auth_method: "query",
         uid_field: "<uid_field>",
         client_options: {
           identifier: "<your_oidc_client_id>",
           secret: "<your_oidc_client_secret>",
           redirect_uri: "<your_gitlab_url>/users/auth/openid_connect/callback",
           gitlab: {
             groups_attribute: "groups",
             required_groups: ["Developer"]
           }
         }
       }
     }
   ]

2. Save the file and reconfigure GitLab for the changes to take effect.

For installation from source:

1. Edit /home/git/gitlab/config/gitlab.yml:

   production: &base
     omniauth:
       providers:
        - { name: 'openid_connect',
            label: 'Provider name',
         args: {
           name: 'openid_connect',
           scope: ['openid','profile','email'],
           response_type: 'code',
           issuer: '<your_oidc_url>',
           discovery: true,
           client_auth_method: 'query',
           uid_field: '<uid_field>',
           client_options: {
             identifier: '<your_oidc_client_id>',
             secret: '<your_oidc_client_secret>',
             redirect_uri: '<your_gitlab_url>/users/auth/openid_connect/callback',
             gitlab: {
               groups_attribute: "groups",
               required_groups: ["Developer"]
             }
           }
         }
       }

2. Save the file and reconfigure GitLab for the changes to take effect.

External groups

Your IdP must pass group information to GitLab in the OIDC response. To use this response to identify users as external users based on group membership, configure GitLab to identify:

• Where to look for the groups in the OIDC response, using the groups_attribute setting.
• Which group memberships should identify a user as an external user, using the external_groups setting.

For Omnibus GitLab:

1. Edit /etc/gitlab/gitlab.rb:

   gitlab_rails['omniauth_providers'] = [
     {
       name: "openid_connect",
       label: "Provider name",
       args: {
         name: "openid_connect",
         scope: ["openid","profile","email"],
         response_type: "code",
         issuer: "<your_oidc_url>",
         discovery: true,
         client_auth_method: "query",
         uid_field: "<uid_field>",
         client_options: {
           identifier: "<your_oidc_client_id>",
           secret: "<your_oidc_client_secret>",
           redirect_uri: "<your_gitlab_url>/users/auth/openid_connect/callback",
           gitlab: {
             groups_attribute: "groups",
             external_groups: ["Freelancer"]
           }
         }
       }
     }
   ]

2. Save the file and reconfigure GitLab for the changes to take effect.

For installation from source:

1. Edit /home/git/gitlab/config/gitlab.yml:

   production: &base
     omniauth:
       providers:
        - { name: 'openid_connect',
            label: 'Provider name',
         args: {
           name: 'openid_connect',
           scope: ['openid','profile','email'],
           response_type: 'code',
           issuer: '<your_oidc_url>',
           discovery: true,
           client_auth_method: 'query',
           uid_field: '<uid_field>',
           client_options: {
             identifier: '<your_oidc_client_id>',
             secret: '<your_oidc_client_secret>',
             redirect_uri: '<your_gitlab_url>/users/auth/openid_connect/callback',
             gitlab: {
               groups_attribute: "groups",
               external_groups: ["Freelancer"]
             }
           }
         }
       }

2. Save the file and reconfigure GitLab for the changes to take effect.

Administrator groups

Your IdP must pass group information to GitLab in the OIDC response. To use this response to assign users as administrator based on group membership, configure GitLab to identify:

• Where to look for the groups in the OIDC response, using the groups_attribute setting.
• Which group memberships grant the user administrator access, using the admin_groups setting.

For Omnibus GitLab:

1. Edit /etc/gitlab/gitlab.rb:

   gitlab_rails['omniauth_providers'] = [
     {
       name: "openid_connect",
       label: "Provider name",
       args: {
         name: "openid_connect",
         scope: ["openid","profile","email"],
         response_type: "code",
         issuer: "<your_oidc_url>",
         discovery: true,
         client_auth_method: "query",
         uid_field: "<uid_field>",
         client_options: {
           identifier: "<your_oidc_client_id>",
           secret: "<your_oidc_client_secret>",
           redirect_uri: "<your_gitlab_url>/users/auth/openid_connect/callback",
           gitlab: {
             groups_attribute: "groups",
             admin_groups: ["Admin"]
           }
         }
       }
     }
   ]

2. Save the file and reconfigure GitLab for the changes to take effect.

For installation from source:

1. Edit /home/git/gitlab/config/gitlab.yml:

   production: &base
     omniauth:
       providers:
        - { name: 'openid_connect',
            label: 'Provider name',
         args: {
           name: 'openid_connect',
           scope: ['openid','profile','email'],
           response_type: 'code',
           issuer: '<your_oidc_url>',
           discovery: true,
           client_auth_method: 'query',
           uid_field: '<uid_field>',
           client_options: {
             identifier: '<your_oidc_client_id>',
             secret: '<your_oidc_client_secret>',
             redirect_uri: '<your_gitlab_url>/users/auth/openid_connect/callback',
             gitlab: {
               groups_attribute: "groups",
               admin_groups: ["Admin"]
             }
           }
         }
       }

2. Save the file and reconfigure GitLab for the changes to take effect.

Troubleshooting

1. Ensure discovery is set to true. If you set it to false, you must specify all the URLs and keys required to make OpenID work.

2. Check your system clock to ensure the time is synchronized properly.

3. As mentioned in the OmniAuth OpenID Connect 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.

4. The OpenID Connect client uses HTTP Basic Authentication to send the OAuth 2.0 access token if client_auth_method is not defined or if set to basic. If you see 401 errors when retrieving the userinfo endpoint, check your OpenID web server configuration. For example, for oauth2-server-php, you may have to add a configuration parameter to Apache.