Web services

Hello, I'm creating an activity module to connect server's lab to moodle to offer students the possibility to remote practices. To do this possible I need to moodle like consumer of the labs web service. I saw the /webservice/(protocol)/lib.php that contains the client of the different supported protocols. My question is: In the constructor i need a token to establish the connection with the external webservice. This token is generated by the external webservice server. How can i used the token in the constructor if the connection is no established?? Thanks!!