A system entity that creates, maintains and manages identity information for principals and also provides authentication services to applications within a federation or distributed network
Identity Providers: Facebook, Amazon, Google, Twitter, GitHub, LinkedIn, etc.
Lightweight Directory Access Protocol (LDAP)
Used to access and maintain distributed directory information services over an IP network
LDAP can also store axillary user data like group membership and roles
OpenID
Open standard and decentralized authentication protocol
OpenID is about providing who are you
OAuth 2.0
Industry-standard protocol for authorization
OAuth doesn’t share password data but instead uses tokens to prove an identity between consumers and service providers
JWT is used for exchanging the tokens between applications
OAuth is about granting access to functionality
SAML
Security Assertion Markup Language is an open standard for exchanging authentication and authorization between an identity provider and a service provider
SAML is used for Single-Sign-On