An authentication gateway is a system component that sits between users and protected services to validate logins. It often talks to directory services such as Active Directory or LDAP, and may broker protocols like RADIUS or MFA workflows before the application grants access. In effect, it becomes a trust boundary: downstream systems accept its decision instead of checking credentials themselves.
This matters because if the gateway is misconfigured or vulnerable, attackers may bypass authentication and reach services that assume the login was legitimate. In real defenses, administrators treat the gateway as critical infrastructure: they restrict network exposure, patch it quickly, review logs for unusual access patterns, and map every service that depends on it. In attacks, a flaw here can have wide impact because one weak gate can protect many internal systems.