<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def init_app(self, app):
 """Setup the 4 default routes."""

        app.add_url_rule(self.request_token_url, view_func=self.request_token,
                         methods=[u'POST'])
        app.add_url_rule(self.access_token_url, view_func=self.access_token,
                         methods=[u'POST'])
        app.add_url_rule(self.register_url, view_func=self.register,
                         methods=[u'GET', u'POST'])
        app.add_url_rule(self.authorize_url, view_func=self.authorize,
                         methods=[u'GET', u'POST'])