code: def authenticate_redirect(self, callback_uri=None, cancel_uri=None,
                                extended_permissions=None):
          
          self.require_setting("facebook_api_key", "Facebook Connect")
          callback_uri = callback_uri or self.request.uri
          args = {
              "api_key": self.settings["facebook_api_key"],
              "v": "1.0",
              "fbconnect": "true",
              "display": "page",
              "next": urljoin(self.request.full_url(), callback_uri),
              "return_session": "true",
          }
          if cancel_uri:
              args["cancel_url"] = urljoin(
                  self.request.full_url(), cancel_uri)
          if extended_permissions:
              if isinstance(extended_permissions, (str, bytes_type)):
                  extended_permissions = [extended_permissions]
              args["req_perms"] = ",".join(extended_permissions)
          self.redirect("http://www.facebook.com/login.php?" +
                        urlencode(args))
docs: Authenticates/installs this app for the current user.