MySQL 5.5.7 and up supports pluggable authentication. Authentication plugins have a server side and a client side. Plugins on the server side implement authentication methods for use by clients when they connect to the server. Plugins on the client client communicate with the corresponding server-side plugin. A client-side plugin may interact with users, performing tasks such as soliciting a password or other authentication credentials to be sent to the server. See Section 5.5.6, “Pluggable Authentication”.

Pluggable authentication also enables proxy user capability, in which one user takes the identity of another user. A server-side authentication plugin can return to the server the name of the user whose identity the connecting user should have. See Section 5.5.7, “Proxy Users”.