In an explicit proxy setup, where is the authentication method and database configured?

A Proxy Policy applies the authentication scheme but does not define the authentication method or database itself.

An Authentication Rule references an authentication scheme to enforce authentication for specific traffic, but it does not configure the underlying method or database.

A Firewall Policy primarily controls network traffic flow and security profiles, and while it can involve authentication, the explicit proxy authentication methods are defined in authentication schemes.

In FortiGate's explicit proxy configuration, an 'Authentication scheme' is the designated place to define the authentication method (e.g., LDAP, RADIUS, local users) and specify the associated database servers. This scheme is then applied by authentication rules or proxy policies to enforce user authentication.