An authentication redirect flow is the login path that sends a user from an application to a sign-in step and then back to the original destination. It often carries return URLs, state values, or similar parameters so the app knows where to send the user after authentication.
This flow matters because it sits on a trust boundary. If input is not validated and output is not encoded correctly, attackers can abuse it for open redirects, token leakage, or reflected cross-site scripting. In real attacks, a crafted link may place malicious data into the redirect handler so the browser renders attacker-controlled content under the site’s origin. Defenders should treat these endpoints as high-risk, validate redirect targets against allowlists, encode all reflected values by context, and keep session handling strict so a flaw in the login path does not become a session-level compromise.