code: def r_oauth_login(self):
          
          session['next'] = request.args.get('next','')
          callback_url = self.authcallback
          if callback_url is None:
              callback_url = url_for('.r_oauth_authorized', _external=True)
          return self.authobj.authorize(callback=callback_url)
docs: Route for OAuth2 Login
  
          :param next next url
          :type str
  
          :return: Redirects to OAuth Provider Login URL