Learn how authorization servers and clients parse OAuth 2.0 callback URLs, validate redirect URIs, extract auth codes, and mitigate CSRF with state parameters.
Frequently Asked Questions
Q1. Why do authorization servers enforce exact redirect URI matching?
If an authorization server allows wildcard or partial matching (e.g. https://example.com/), an attacker can redirect the authorization code or token to an open redirect endpoint on that domain to steal user sessions.
Q2. Why are tokens passed in the hash fragment (#) in Implicit flow?
Hash fragments are strictly processed client-side by browsers and are never transmitted in HTTP request headers or logged in web server access logs, reducing token exposure.
Q3. How do I extract parameters from a callback URL with a hash fragment?
Pass window.location.hash.substring(1) into new URLSearchParams(window.location.hash.substring(1)) to parse access_token, token_type, and expires_in.