Callback decorator to require HTTP auth (basic).
        TODO: Add route(check_auth=...) parameter.

def auth_basic(check, realm="private", text="Access denied"):
    ''' Callback decorator to require HTTP auth (basic).
        TODO: Add route(check_auth=...) parameter. '''
    def decorator(func):
      def wrapper(*a, **ka):
        user, password = request.auth or (None, None)
        if user is None or not check(user, password):
          response.headers['WWW-Authenticate'] = 'Basic realm="%s"' % realm
          return HTTPError(401, text)
        return func(*a, **ka)
      return wrapper
    return decorator