class type auth_session =object..end
auth_session represents an authenticated sessionmethod auth_scheme : stringmethod auth_domain : Neturl.url list * int
        The integer is the transport layer ID.
method auth_realm : stringmethod auth_user : stringmethod authenticate : http_call ->
       bool -> (string * string) list auth_statusauthorization.)
 If a re-authentication needs to be done, the call does not contain
 any authentication information. If the call is authenticated
 in reaction to a 401 status, the response header contains 
 the www-authenticate field(s).
 The bool says whether this is the re-authentication path.
method auth_session_id : string optionauthenticate. After a re-authentication
         the ID may change.method invalidate : http_call -> unit