Understanding Federated Identity Management: Concepts, Roles, Benefits, and Use Cases

Introduction

Federated identity management (FIM) is an arrangement that allows users from two or more trusted domains to use the same digital identity to access applications and services, a concept known as identity federation.

FIM builds on trust between domains such as partner organizations, business units, or subsidiaries, and is typically delegated to an identity broker service provider that mediates access control across multiple providers.

The broker may be referred to by various names (identity provider, resident identity provider, federated identity provider, federated provider, or persistent authorization server) depending on its role in the federation.

Roles in Identity Federation

Identity Provider – issues digital identities with claims for service providers.

Resident Identity Provider – defines digital identities but does not issue them within its trust domain.

Federated Identity Provider – defined for a trust domain and issues identities belonging to a second trust domain, establishing a trust relationship.

Federated Provider – the identity broker that mediates IAM operations across multiple service providers and identity providers.

Persistent Authorization Server – defined for a service provider and authenticates/authorizes access requests.

Benefits of Identity Federation

Seamless user experience with a single set of credentials.

Most implementations support single sign‑on (SSO).

Reduces management overhead by delegating account and password responsibilities to a resident identity provider.

Simplifies data management and storage costs.

Alleviates privacy and compliance burdens.

Federated Identity Management Use‑Case Examples

Provides access to users from vendors, distributors, and partner networks.

Enables access for new users after mergers and acquisitions.

Allows access to users from commercial identity providers such as banks (e.g., PSD2 third‑party payment providers).

Uses national identity providers (e.g., DigiD, Emirates ID) to grant citizen access.

Supports users with public organization IDs (e.g., ORCID).

Enables social login (Facebook, Google, LinkedIn, etc.).

Can serve as a temporary arrangement to support IAM system migration.

Inbound and Outbound Identity Federation

Inbound federation occurs when an identity broker receives assertions from another broker, allowing access to applications beyond the broker's own trust boundary.

Outbound federation is when an identity provider generates assertions for use by another broker, enabling the latter to grant access to external applications.

Figure 1: Identity federation between an enterprise and a SaaS application hosted in Azure, where the enterprise acts as the tenant and federated provider.

Identity Federation vs. Single Sign‑On

Most federation solutions implement SSO so users do not need to re‑authenticate for each session, but SSO is not synonymous with federation; some SSO implementations (e.g., Kerberos‑based Integrated Windows Authentication) are not considered federation.

Bring Your Own Identity (BYOID)

BYOID refers to using a social or external identity for registration, login, or account linking, extending beyond social contexts to government, NGO, or enterprise‑issued digital identities.

Use‑case 3‑6 in the article illustrate BYOID for customer IAM (CIAM), with distinct goals for registration, login, and connection.

Federated Account Linking

Federated account linking ties a single digital identifier from multiple federated identity providers to a persistent identifier in a resident identity provider, enabling richer account, password, and rights management.

Figure 2: Federated login without account linking.

Figure 3: Federated login with account linking.

Just‑In‑Time (JIT) Account Provisioning

JIT account provisioning creates user accounts on the fly within an intermediate identity broker, a key component of JIT account linking.

Figure 4: Federated login with JIT account provisioning.

Just‑In‑Time Password Provisioning

JIT password provisioning is an optional step to the JIT account provisioning process, depending on organizational password policies and the applications being accessed.

Home Realm Discovery (HRD)

HRD identifies the resident identity provider for a specific user, enabling authentication and claim issuance; it can be automatic or involve user interaction.

Common HRD methods include presenting a list of options, identifier‑first login, selective realm discovery, query‑parameter hints, IP‑based routing, header injection, cookies, and nested federation scenarios.

Supporting IAM Migration

Federated identity can serve as a transitional strategy for migrating from multiple disparate user directories to a single consolidated directory, optionally providing passwords during the migration phase.

Summary

The article outlines the fundamentals of federated identity management, its roles, benefits, and typical use cases. While many protocols (SAML2, OpenID Connect, WS‑Trust, WS‑Federation) can implement federation, the concepts remain consistent across implementations.

WSO2 Identity Server, an open‑source IAM product, exemplifies a platform capable of acting in any broker role described.