How do you handle federation and interoperability between OAuth, SAML, and OpenID?

1 What is OAuth?

OAuth is an open standard for authorization that allows users to grant access to their resources on one platform to another platform without sharing their credentials. For example, you can use OAuth to let a third-party app access your Google Drive files or your Facebook photos. OAuth uses tokens to represent the scope and duration of the access granted by the user. OAuth is not an authentication protocol, meaning it does not verify the identity of the user, but it relies on other methods, such as OpenID Connect, to do so.

2 What is SAML?

SAML stands for Security Assertion Markup Language, and it is an XML-based standard for authentication and authorization. SAML enables single sign-on (SSO), which means users can log in once to a central identity provider (IdP) and access multiple service providers (SPs) without entering their credentials again. For example, you can use SAML to log in to your company's intranet and access various applications and services. SAML uses assertions to exchange information about the user's identity, attributes, and permissions between the IdP and the SPs.

4 How do they compare?

OAuth, SAML, and OpenID have different purposes, architectures, and formats, but they all share some commonalities and overlaps. OAuth is mainly used for authorization, SAML is mainly used for authentication and authorization, and OpenID is mainly used for authentication. OAuth utilizes a client-server model where the client requests access to the user's resources on the server. SAML uses a federated model with the IdP and SPs trusting each other and exchanging assertions. OpenID uses a decentralized model where the user chooses their OP and the RP accepts it. OAuth utilizes JSON or URL-encoded tokens, SAML uses XML-based assertions, and OpenID uses URL or URI identifiers. OAuth relies on HTTPS and TLS for security, as well as optionally supporting encryption and digital signatures. SAML implements XML encryption and digital signatures for security. OpenID also utilizes HTTPS and TLS for security, with optional encryption and digital signatures available. OAuth is relatively simple and flexible but has multiple versions and extensions that can lead to confusion or inconsistency. SAML is relatively complex but has a well-defined specification that can ensure interoperability and compliance. OpenID is simple but has limited functionality and adoption.