OAuth 2.0
Also called: OAuth, OpenID Connect
A standard that lets an app get limited access to a user's data on another service without seeing their password.
Definition
OAuth 2.0 is an authorization framework: the user approves access, and the app receives an access token limited by scopes. "Sign in with Google" adds OpenID Connect on top of OAuth to also tell the app who the user is. Testers usually test the result: the login flow, the token's scopes, and that endpoints refuse tokens without the needed scope.
In practice
A fitness app asks for permission to read your steps from another service, but not your contacts; its token only has the steps scope.
Learn it in context
Lessons that use this term.