class type auth_method =object..end
auth_method object represents a method of authentication. Such an
 object can be shared by several clients.method name : stringmethod new_session : t -> string option -> auth_protocolNone
	     if the default is to be used (whatever this is). Some
	     authenticators only support None.
	     It is allowed that the returned auth_protocol object is already
	     in state `Done, i.e. that actually no protocol is run.
	     Changed in Ocamlnet-3.3: different signature. The user name is
	     now an argument, and the method returns auth_protocol instead
	     of auth_session. There can now be a separate session for
	     each user (plus for the default user None).