OAuth2 Proxy is an authentication reverse proxy placed in front of upstream applications. It checks whether a user is allowed to reach the backend, usually by integrating with an identity provider and then forwarding trusted identity information to the app. This lets teams add centralized login and access control without changing each application individually.
It matters in cyber security because it creates a powerful trust boundary at the edge. If the proxy accepts forged or overtrusted headers, or if skip-auth routes and allow-lists are too broad, an attacker may bypass authentication and reach protected services as if already logged in. Defenders therefore treat proxy-supplied metadata as sensitive, restrict which network sources can influence it, and review configuration carefully. In real environments, OAuth2 Proxy is often used to protect internal dashboards, admin panels, and APIs, so one mistake can expose many upstream systems at once.