code: func (s *DefaultCookieProtector) DecodeToken(p []byte) ([]byte, error) {
  	if len(p) < cookieNonceSize {
  		return nil, fmt.Errorf("Token too short: %d", len(p))
  	}
  	nonce := p[:cookieNonceSize]
  	aead, aeadNonce, err := s.createAEAD(nonce)
  	if err != nil {
  		return nil, err
  	}
  	return aead.Open(nil, aeadNonce, p[cookieNonceSize:], nil)
  }
docs: // DecodeToken decodes a token.