OAuth

Match OAuth Redirect URIs Exactly

An OAuth authorization server eventually has to answer a deceptively simple question: where may it send the browser after authorization? If that destination is validated too loosely, an authorization response intended for one client can be sent somewhere the client does not control. In an authorization-code flow, that can expose the authorization code to another endpoint. Other protections may still limit what can be done with a leaked code, but redirect validation should not create the leak in the first place.