Federation Pass-through Authentication (PTA)

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🌐 What is Federation Pass-through Authentication (PTA)?

Federation Pass-through Authentication (PTA) is a method that combines Pass-through Authentication (PTA) with Federation (e.g., Active Directory Federation Services, ADFS). It allows you to authenticate users using your on-premises Active Directory (AD), but without storing passwords in Azure AD and without relying on the full federation infrastructure like ADFS.

🧠 How Does Federation Pass-through Authentication Work?

Here’s how the Federation PTA flow works:

  1. User attempts to log in to a cloud application (e.g., Microsoft 365).

  2. Azure AD receives the authentication request.

  3. Azure AD checks if Pass-through Authentication is configured.

    • If yes, it forwards the authentication request to your on-premises AD.

  4. The on-premises AD server verifies the user credentials using the Federation Server (like ADFS or a PTA agent).

  5. If the credentials are correct, the user is granted access to the cloud application.

Unlike a traditional federation setup where Azure AD directly interacts with ADFS, Federation PTA leverages the PTA agent for authentication.

🔧 Key Components of Federation Pass-through Authentication:

  1. Azure AD Connect: The tool used to sync and configure PTA.

  2. PTA Agent: Installed on-premises, this agent passes the authentication request from Azure AD to your on-prem AD or federation server.

  3. Federation Server (like ADFS): The server that validates user credentials for on-premises users. In Federation PTA, the PTA agent uses this for authenticating the user.

🧰 Benefits of Federation Pass-through Authentication (PTA):

BenefitDescription
✅ No Passwords Stored in the CloudPasswords are never stored in Azure AD. Azure only passes the authentication request to on-prem AD.
✅ Federated SecurityLeverages your existing on-premises federation infrastructure (like ADFS) to validate users.
✅ Hybrid IdentityPerfect for organizations that want to have a mix of cloud and on-prem authentication without fully migrating their authentication to the cloud.
✅ Easy Setup with Azure AD ConnectSimple to configure using Azure AD Connect for synchronization and authentication passing.
✅ Supports Single Sign-On (SSO)Users can log in seamlessly with the same credentials to both cloud and on-prem resources.

🆚 Federation PTA vs. Full Federation (e.g., ADFS)

FeatureFederation PTAFull Federation (e.g., ADFS)
Where Authentication HappensOn-premises (via PTA Agent)On-premises (via ADFS server)
Need for Federation InfrastructureMinimal (requires PTA agent, no full ADFS setup)Full ADFS setup and federation infrastructure
Password StoragePasswords are not stored in Azure ADPasswords are not stored in Azure AD
Dependency on On-prem ServersDependent on the availability of PTA agents and on-prem ADDependent on ADFS servers for authentication
ComplexitySimpler, easier setupMore complex to set up and maintain

💡 When Should You Use Federation Pass-through Authentication (PTA)?

Federation PTA is ideal in the following scenarios:

  • You want to keep on-premises authentication (with existing Federation setup) while moving to the cloud for services like Office 365.

  • You don’t want the complexity of setting up ADFS servers and their associated infrastructure.

  • You need a hybrid solution that combines local identity management with cloud applications but without syncing passwords to the cloud.

🔐 Real-life Example:

A company uses Active Directory Federation Services (ADFS) for managing on-prem authentication but wants to enable cloud access for its employees to Office 365. They don’t want to manage a full ADFS solution in the cloud, so they implement Federation Pass-through Authentication (PTA). This way, Azure AD uses their on-prem ADFS infrastructure via the PTA agent to authenticate users while maintaining all passwords securely on-prem.

🧩 Summary of Benefits:

  • No Password Syncing: Credentials are never stored in Azure AD.

  • Familiar Federation Setup: You can use your existing ADFS infrastructure for authentication.

  • Hybrid Model: Ideal for organizations that want cloud integration but still depend on their on-prem AD.

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