code: def init_app(self, app, **kwargs):
          
          self.init_config(app)
  
          allowed_urlencode_chars = app.config.get(
              'OAUTH2SERVER_ALLOWED_URLENCODE_CHARACTERS')
          if allowed_urlencode_chars:
              InvenioOAuth2ServerREST.monkeypatch_oauthlib_urlencode_chars(
                  allowed_urlencode_chars)
          app.before_request(verify_oauth_token_and_set_current_user)
docs: Flask application initialization.
  
          :param app: An instance of :class:`flask.Flask`.