docs: def dispatch_request(self):
          """ Handle redirect back from provider """
          if current_user.is_authenticated:
              return redirect(self.next)
  
          # clear previous!
          if 'social_data' in session:
              del session['social_data']
  
          res = self.app.authorized_response()
          if res is None:
              if self.flash: flash(self.auth_failed_msg, 'danger')
              return redirect(self.next)
  
          # retrieve profile
          data = self.get_profile_data(res)
          if data is None:
              if self.flash: flash(self.data_failed_msg, 'danger')
              return redirect(self.next)
  
          # attempt login
          try:
              ok = user_service.attempt_social_login(self.provider, data['id'])
              if ok:
                  if self.flash:
                      flash(self.logged_in_msg.format(self.provider), 'success')
                  return redirect(self.logged_in)
          except x.AccountLocked as locked:
              msg = self.lock_msg.format(locked.locked_until)
              if self.flash: flash(msg, 'danger')
              url = url_for(self.lock_redirect, **self.lock_redirect_params)
              return redirect(url)
          except x.EmailNotConfirmed:
              return redirect(url_for(self.unconfirmed_email_endpoint))
  
          # get data
          email = data.get('email')
          provider = data.get('provider')
          id = data.get('id')
          id_column = '{}_id'.format(provider)
  
          # user exists: add social id to profile
          user = user_service.first(email=email)
          if user:
              setattr(user, id_column, id)
              user_service.save(user)
  
          # no user: register
          if not user:
              cfg = current_app.config
              send_welcome = cfg.get('USER_SEND_WELCOME_MESSAGE')
              base_confirm_url = cfg.get('USER_BASE_EMAIL_CONFIRM_URL')
              if not base_confirm_url:
                  endpoint = 'user.confirm.email.request'
                  base_confirm_url = url_for(endpoint, _external=True)
  
              data = dict(email=email)
              data[id_column] = id
              user = user_service.register(
                  user_data=data,
                  send_welcome=send_welcome,
                  base_confirm_url=base_confirm_url
              )
  
          # email confirmed?
          if user_service.require_confirmation and not user.email_confirmed:
              return redirect(url_for(self.ok_endpoint, **self.ok_params))
  
          # otherwise just login
          user_service.force_login(user)
          return redirect(self.force_login_redirect)