Active Directory Federation Services support in MSAL.NET

Active Directory Federation Services (AD FS) in Windows Server enables you to add OpenID Connect and OAuth 2.0 based authentication and authorization to applications you are developing. Those applications can, then, authenticate users directly against AD FS. For more information, read AD FS Scenarios for Developers.

Microsoft Authentication Library for .NET (MSAL.NET) supports two scenarios for authenticating against AD FS:

  • MSAL.NET talks to Azure Active Directory, which itself is federated with AD FS.
  • MSAL.NET talks directly to an ADFS authority. This is only supported from AD FS 2019 and above. One of the scenarios this highlights is Azure Stack support

MSAL connects to Azure AD, which is federated with AD FS

MSAL.NET supports connecting to Azure AD, which signs in managed-users (users managed in Azure AD) or federated users (users managed by another identity provider such as AD FS). MSAL.NET does not know about the fact that users are federated. As far as it’s concerned, it talks to Azure AD.

The authority you use in this case is the usual authority (authority host name + tenant, common, or organizations).

Acquiring a token interactively

When you call the AcquireTokenInteractive method, the user experience is typically:

  1. The user enters their account ID.
  2. Azure AD displays briefly the message "Taking you to your organization's page".
  3. The user is redirected to the sign-in page of the identity provider. The sign-in page is usually customized with the logo of the organization.

Supported AD FS versions in this federated scenario are AD FS v2, AD FS v3 (Windows Server 2012 R2), and AD FS v4 (AD FS 2016).

Acquiring a token using AcquireTokenByIntegratedAuthentication or AcquireTokenByUsernamePassword

When acquiring a token using the AcquireTokenByIntegratedAuthentication or AcquireTokenByUsernamePassword methods, MSAL.NET gets the identity provider to contact based on the username. MSAL.NET receives a SAML 1.1 token after contacting the identity provider. MSAL.NET then provides the SAML token to Azure AD as a user assertion (similar to the on-behalf-of flow) to get back a JWT.

MSAL connects directly to AD FS

MSAL.NET supports connecting to AD FS 2019, which is Open ID Connect compliant and understands PKCE and scopes. This support requires that a service pack KB 4490481 is applied to Windows Server. When connecting directly to AD FS, the authority you'll want to use to build your application is similar to https://mysite.contoso.com/adfs/.

Currently, there are no plans to support a direct connection to:

  • AD FS 16, as it doesn't support PKCE and still uses resources, not scope
  • AD FS v2, which is not OIDC-compliant.

If you need to support scenarios requiring a direct connection to AD FS 2016, use the latest version of Azure Active Directory Authentication Library. When you have upgraded your on-premises system to AD FS 2019, you'll be able to use MSAL.NET.

Next steps

For the federated case, see Configure Azure Active Directory sign in behavior for an application by using a Home Realm Discovery policy