OAUTH + OPENID

OAUTH — Delegated Authorization protocol. Basically you want to expose your permissions(scopes) of your resource(api) to outside world. You need a resource(contacts.google.com) permissions(read,update etc) and identity ( accounts.google.com)

OPENID — Built on top of OAUTH as people are using OAUTH for AUTHENTICATION. When calling resource server, scope set to OPENID and resource server will return ID_TOKEN (AUTHENTICATION) along with…