This performs a similar function to oauth_listener
,
but without trying do open a browser or start a local webserver.
This manual process can be useful in situations where the user is
remotely accessing the machine outside a browser (say via ssh) or
when it's not possible to successfully receive a callback (such as
when behind a firewall).
oauth_exchanger(request_url)
the url to provide to the user
This function should generally not be called directly by the user.