5.2. The "none" Authentication Request

A client may request a list of authentication 'method name' values that may continue by using the "none" authentication 'method name'.

If no authentication is needed for the user, the server MUST return SSH_MSG_USERAUTH_SUCCESS. Otherwise, the server MUST return SSH_MSG_USERAUTH_FAILURE and MAY return with it a list of methods that may continue in its 'authentications that can continue' value.

This 'method name' MUST NOT be listed as supported by the server.