OAuth 2.0 OpenID

OAuth 2.0 is the industry standard for authorization (granting third-party applications access to user data without sharing passwords). OpenID Connect is an identity layer built on OAuth 2.0 for authentication (proving who a user is). Together, they enable "Sign in with Google," "Login via GitHub," and similar patterns. The flow: user clicks "Login with Google" → redirected to Google → user grants permission → redirected back with access token → app uses token to access user data. User never shares password; only Google knows it.