User federation refers to the process of connecting and integrating multiple identity systems or directories, allowing users to authenticate and access resources across different systems or organizations using a single identity. It enables interoperability between various identity providers, facilitating a Single Sign-On (SSO) experience for users.

In other words, user federation allows an organization to accept and manage user identities from external systems (e.g., from another company, a third-party service, or a cloud provider) while maintaining consistent access control and authentication.

Key Features of User Federation

• Cross-Organization Authentication: User federation allows users from one identity provider (e.g., Active Directory, Google, or Facebook) to access applications or resources in another system without needing to create separate accounts.
• Single Sign-On (SSO): By federating identities, users only need to authenticate once to access multiple systems or services that trust the federated identity provider.
• Standard Protocols: Federation often uses open standards and protocols like SAML (Security Assertion Markup Language), OAuth, and OpenID Connect to facilitate secure identity exchange and authentication between systems.
• Security and Trust: Federation establishes trust relationships between identity providers and service providers to ensure that identity information is accurately exchanged and validated, maintaining security and privacy.

Common Use Cases for User Federation

• Business-to-Business (B2B) Collaboration: When organizations need to allow external partners or vendors to access internal systems securely, user federation enables those external users to use their existing credentials (e.g., from their company’s AD or identity provider) without creating new accounts.
• Cloud Service Access: User federation allows users to authenticate with their organization's directory (e.g., Active Directory) to access cloud-based services like Microsoft 365 or AWS.
• Social Login: Many applications allow users to log in using their social media accounts (e.g., Google, Facebook, or LinkedIn) through user federation, eliminating the need to create a separate account for each service.

Key Differences Between User Directory and User Federation: