Federated authentication is a method of linking a user’s identity across multiple separate identity management systems, allowing them to seamlessly access multiple platforms using a single set of credentials. This approach to identity management helps to improve the user experience and increase security by eliminating the need for multiple usernames and passwords.

OpenID Connect, OAuth 2.0, and Security Assertion Markup Language (SAML) are three widely used technologies in federated authentication.

OpenID Connect is an open standard for authentication that allows users to log in to an identity provider (IdP) and access other websites and applications without having to log in again. It is built on top of OAuth 2.0 and provides a secure, convenient way for users to authenticate with an IdP and share their identity with service providers. The process works by prompting the user to log in to their IdP account, such as Google, and authorize the service provider to access their data. The IdP then issues a token to the service provider, allowing the user to access their account without having to log in again. The protocol defines a set of standard messages and endpoints, providing interoperability between different systems. The core of the protocol is the ID Token, a JSON Web Token that contains information about the authenticated user.

OAuth 2.0 is an authorization framework that allows users to give third-party apps access to their resources without sharing their credentials. It defines four roles: resource owner, client, resource server, and authorization server. The resource owner is the user who owns the resources, and the client is the third-party application that wants to access them. The resource server holds the resources and the authorization server authenticates the user and issues access tokens. OAuth 2.0 defines several grant types such as authorization code grant and implicit grant which can be used to obtain access tokens in different scenarios. It is an open standard for authorization that enables users to share their resources, such as data or access to an application with a third-party application without having to share their login credentials. It is commonly used when a user wants to connect a new application to their social media account, such as Facebook or Twitter, where the user’s social media account acts as the identity provider (IdP) and issues a token to the third-party application, allowing it to access the user’s data in a secure way.

SAML (Security Assertion Markup Language) is an XML-based standard for exchanging authentication and authorization data between identity providers (IdPs) and service providers. It defines several message types and bindings to authenticate users, request and grant access to resources, and manage sessions. It is commonly used in enterprise environments where a single set of credentials is used to authenticate users across multiple applications. A common use case for SAML is when a user wants to access multiple services within a corporate network, such as Salesforce or Workday, using a single set of login credentials. The user logs in to the corporate intranet or IdP, which acts as the IdP, and then accesses the other services without having to log in again. The IdP verifies the user’s identity and permissions and grants or denies access to the services, providing a secure and convenient way for the user to access multiple services within a corporate network without having to remember multiple usernames and passwords.

The main difference between OpenID Connect, OAuth 2.0, and SAML is their focus and scope. OpenID Connect is focused on user authentication and the ID Token is the core of the protocol. OAuth 2.0 is focused on authorization and access to resources, and SAML is focused on enterprise single sign-on and exchanging authentication and authorization data between systems. When deciding which protocol to use for federated authentication, it’s important to consider the requirements of your specific use case. OpenID Connect is a good choice for consumer-facing applications that need to authenticate users and provide access to their resources. OAuth 2.0 is a good choice for applications that need to access resources on behalf of a user, but don’t need to authenticate the user themselves. SAML is a good choice for enterprise environments where there is a need to authenticate users across multiple applications using a single set of credentials.

In conclusion, federated authentication using OpenID Connect, OAuth 2.0, and SAML are powerful approaches to identity management that can improve the user experience, increase security, and reduce administrative overhead. However, it is important to carefully evaluate the potential risks and benefits of each protocol before implementing it in your organization and to select the appropriate protocol for your use case.