Handle post request.

def post(self):
    """Handle post request."""
    template_values = {
        'back_url': '/showCredentials',
        'back_msg': 'View Credentials',
        'logout_url': users.create_logout_url('/'),
        'user_nickname': users.get_current_user().nickname()
    }
    try:
      UpdateUserCredentials(self.request.get('client_id'),
                            self.request.get('client_secret'),
                            self.request.get('refresh_token'),
                            self.request.get('adwords_manager_cid'),
                            self.request.get('dev_token'))
      self.redirect('/showCredentials')
    except Exception, e:
      template_values['error'] = str(e)
      # Use template to write output to the page.
      path = os.path.join(os.path.dirname(__file__),
                          '../templates/base_template.html')
      self.response.out.write(template.render(path, template_values))