code: def oauth_signup(self, provider, attrs, defaults, redirect_url=None):
          
          session["oauth_user_defaults"] = defaults
          session["oauth_user_attrs"] = dict(provider=provider, **attrs)
          if not redirect_url:
              redirect_url = request.args.get("next")
          return redirect(url_for('users.oauth_signup', next=redirect_url))
docs: Start the signup process after having logged in via oauth