Configure Workload Identity Federation with Active Directory

This guide describes how to use Workload Identity Federation to let workloads use Active Directory credentials to authenticate to Google Cloud.

If you're running Windows Server workloads in an Active Directory environment, then these workloads might have access to Active Directory credentials. For example:

  • A Windows Service might be configured to log on as a domain user.
  • An IIS application might be configured to run as a group managed service account (gMSA).

By using Workload Identity Federation in combination with Active Directory Federation Services (AD FS), you can let these workloads exchange their Active Directory Kerberos credentials for short-lived Google Cloud credentials. Workloads can use these short-lived credentials to access Google Cloud APIs.

Exchanging Active Directory credentials against short-lived Google Cloud credentials works by chaining two token exchanges:

  1. A workload uses OpenID Connect (OIDC), SAML-POST, or WS-Trust to request an OIDC token or SAML assertion from AD FS. To authenticate to AD FS, the workload uses integrated Windows authentication (IWA) and its existing Active Directory credentials.
  2. The workload then uses Workload Identity Federation to exchange the OIDC token or SAML assertion against an Security Token Service token and, optionally, to impersonate a Google Cloud service account.

This document shows you how you can automate this process in a way that doesn't require changes to your application by using the Workload Authenticator for Windows.

Prepare AD FS

You only need to perform these steps once.

Select a protocol

The way to prepare AD FS depends on which protocol you want to use:

  • SAML: You can let workloads use SAML or WS-Trust to obtain SAML assertions.

    To use SAML or WS-Trust, you create a relying party in AD FS and configure a workload identity pool to trust assertions issued for this relying party.

    A workload can use its Active Directory user to authenticate to AD FS either by using the SAML-POST binding or WS-Trust. AD FS then issues a SAML assertion that contains information about the workload's Active Directory user and additional information such as group memberships.

    Using SAML or WS-Trust requires AD FS 3.0, AD FS for Windows Server 2016, or a newer version of AD FS.

  • OIDC: You can let workloads use OIDC to obtain OIDC tokens.

    To use OIDC, you create an OIDC client (native application) and an OIDC resource (Web API) in AD FS. You then configure a workload identity pool to trust access tokens issued for the Web API.

    A workload can use its Active Directory user and the OAuth client_credentials grant to authenticate to AD FS. AD FS then issues an access token, but no ID token.

    The access token contains information about the OIDC client application, but doesn't include any information about the workload's Active Directory user or its group memberships.

    Because access tokens don't contain any information about the Active Directory user, using OIDC can be less flexible than using SAML or WS-Trust.

    Using OIDC requires AD FS for Windows Server 2016 or a newer version of AD FS.

For sign-in, your IdP must provide signed authentication information: OIDC IdPs must provide a JWT, and SAML IdP responses must be signed.

IWA prerequisites

This section describes IWA prerequisites that are required in order to use this guide.

If you haven't used IWA with AD FS before, make sure that you meet the following prerequisites:

Register the workload

To register your workload in AD FS, do the following:

OIDC

To let workloads use OIDC, you need two application registrations in AD FS:

  • An application registration of type native application or server application.

  • An application registration of type Web API that corresponds to a workload identity pool provider on Google Cloud.

Registering the client application

Create a client application that represents the workload. If you have multiple workloads that need access to Google Cloud, you might need to create multiple client applications.

To register a client application in AD FS, do the following:

  1. Open the AD FS MMC snap-in and navigate to Application Groups.
  2. Click Add application group.

  3. On the Welcome page, do the following:

    1. In the text field, enter a name for the client.
    2. Select Server application.
    3. Click Next.

  4. On the Server application page, do the following:

    1. In the text-field text field, enter a client identifier (Client ID) and a redirect URI.

      If you're only planning to use the client_credentials grant type, the redirect URI won't be used and you can use a URI such as http://localhost/.

    2. Click Next.

  5. On the Configure application credentials page, do the following:

    1. Choose how the client authenticates. To use IWA, set Windows Integrated Authentication to enabled.
    2. Select the domain user that your application is configured to run as.
    3. Click Next.

  6. On the Summary page, review the settings and click Next.

  7. Click Close to dismiss the dialog.

Creating a Web API application for the workload identity pool

Create another application registration of type Web API. This application corresponds to a workload identity pool provider, and you use it to set up a trust relationship to Google Cloud.

To create the application in AD FS, do the following:

  1. Open the AD FS MMC snap-in and navigate to Application Groups.
  2. Click Add application group.
  3. On the Welcome page, enter a name such as Workload Identity Federation (test environment) and select Web API. Then click Next.

  4. On the Configure Web API page, enter a relying party identifier for the Web API.

    Instead of defining a custom relying party identifier, you can use the following URI as relying party identifier:

    https://iam.googleapis.com/projects/PROJECT_NUMBER/locations/global/workloadIdentityPools/WORKLOAD_POOL_ID/providers/WORKLOAD_PROVIDER_ID