Authentication Through Google

Overview

Dex is able to use Google’s OpenID Connect provider as an authentication source.

The connector uses the same authentication flow as the OpenID Connect provider but adds Google specific features such as Hosted domain support and reading groups using a service account.

Configuration

connectors:
- type: google
  id: google
  name: Google
  config:

    # Connector config values starting with a "$" will read from the environment.
    clientID: $GOOGLE_CLIENT_ID
    clientSecret: $GOOGLE_CLIENT_SECRET

    # Dex's issuer URL + "/callback"
    redirectURI: http://127.0.0.1:5556/callback

    # Set the value of `prompt` query parameter in the authorization request
    # The default value is "consent" when not set.
    # promptType: consent

    # Google supports whitelisting allowed domains when using G Suite
    # (Google Apps). The following field can be set to a list of domains
    # that can log in:
    #
    # hostedDomains:
    #  - example.com

    # The Google connector supports whitelisting allowed groups when using G Suite
    # (Google Apps). The following field can be set to a list of groups
    # that can log in:
    #
    # groups:
    #  - admins@example.com

    # Google does not support the OpenID Connect groups claim and only supports
    # fetching a user's group membership with a service account.
    # This service account requires an authentication JSON file and the email
    # of a G Suite admin to impersonate:
    #
    #serviceAccountFilePath: googleAuth.json
    #domainToAdminEmail:
    #  *: super-user@example.com
    #  my-domain.com: super-user@my-domain.com

Fetching groups from Google

To allow Dex to fetch group information from Google, you will need to configure a service account for Dex to use. This account needs Domain-Wide Delegation and permission to access the https://www.googleapis.com/auth/admin.directory.group.readonly API scope.

To get group fetching set up:

  1. Follow the instructions to set up a service account with Domain-Wide Delegation
  • During service account creation, a JSON key file will be created that contains authentication information for the service account. This needs storing in a location accessible by Dex and you will set the serviceAccountFilePath to point at it.
  • When delegating the API scopes to the service account, delegate the https://www.googleapis.com/auth/admin.directory.group.readonly scope and only this scope. If you delegate more scopes to the service account, it will not be able to access the API.
  1. Enable the Admin SDK
  2. Add the serviceAccountFilePath and domainToAdminEmail configuration options to your Dex config.
  • serviceAccountFilePath should point to the location of the service account JSON key file
  • domainToAdminEmail should map the base domain to the email address of a Google Workspace user with a minimum of the Groups Reader (BETA) Role assigned. The service account you created earlier will impersonate this user when making calls to the admin API. A valid user should be able to retrieve a list of groups when testing the API.

Dex will set prompt=consent by default when redirecting users to Google’s authorization endpoint. This will force users to see the consent screen every time they log in.

To change this behavior, you can set the promptType field in config file to any OIDC-supported value. To skip the consent screen for every authorization request, set promptType to "" (empty string) to fall back to Google’s default behavior.