# Signals

Flask-Dance supports signals, just as Flask does. Signals are perfect for custom processing code that you want to run at a certain point in the OAuth dance. For example, after the dance is complete, you might need to update the user’s profile, kick off a long-running task, or simply flash a message to let the user know that the login was successful. It’s easy, just import the appropriate signal of the ones listed below, and connect your custom processing code to the signal.

The following signals exist in Flask-Dance:

flask_dance.consumer.oauth_before_login

  Added in version 1.4.0.

  This signal is sent before redirecting to the provider login page. The signal is sent with a `url` parameter specifying the redirect URL. This signal is mostly useful for doing things like session construction/deconstruction before the user is redirected.

  Example subscriber:

      import flask
      from flask_dance.consumer import oauth_before_login

      @oauth_before_login.connect
      def before_login(blueprint, url):
          flask.session["next_url"] = flask.request.args.get("next_url")

flask_dance.consumer.oauth_authorized

  This signal is sent when a user completes the OAuth dance by receiving a response from the OAuth provider’s authorize URL. The signal is invoked with the blueprint instance as the first argument (the sender), and with a dict of the OAuth provider’s response (the token).

  Example subscriber:

      from flask import flash
      from flask_dance.consumer import oauth_authorized

      @oauth_authorized.connect
      def logged_in(blueprint, token):
          flash("Signed in successfully with {name}!".format(
              name=blueprint.name.capitalize()
          ))

  If you are linking OAuth records to User records, you must implement an `@oauth_authorized` subscriber that creates new `User` and `OAuth` database entries for any new users, and links those two new records via the `OAuth` table’s `user_id` field.

  If you’re using OAuth 2, the user may grant you different scopes from the ones you requested: check the `scope` key in the token dict to determine what scopes were actually granted. If you don’t want the token to be stored, simply return `False` from one of your signal receiver functions – this can be useful if the user has declined to authorize your OAuth request, has granted insufficient scopes, or in some other way has given you a token that you don’t want.

  You can also return a `Response` instance from an event subscriber. If you do, that response will be returned to the user instead of the normal redirect. For example:

      from flask import redirect, url_for

      @oauth_authorized.connect
      def logged_in(blueprint, token):
          return redirect(url_for("after_oauth"))

flask_dance.consumer.oauth_error

  This signal is sent when the OAuth provider indicates that there was an error with the OAuth dance. This can happen if your application is misconfigured somehow. The user will be redirected to the `redirect_url` anyway, so it is your responsibility to hook into this signal and inform the user that there was an error.

  You can also return a `Response` instance from an event subscriber. If you do, that response will be returned to the user instead of the normal redirect. For example:

      from flask import redirect, url_for

      @oauth_error.connect
      def handle_error(blueprint, error, error_description=None, error_uri=None):
          return redirect(url_for("custom_error_page"))