code: func NewSecretsVerifier(header http.Header, secret string) (sv SecretsVerifier, err error) {
  	var (
  		timestamp int64
  	)
  
  	stimestamp := header.Get(hTimestamp)
  
  	if sv, err = unsafeSignatureVerifier(header, secret); err != nil {
  		return SecretsVerifier{}, err
  	}
  
  	if timestamp, err = strconv.ParseInt(stimestamp, 10, 64); err != nil {
  		return SecretsVerifier{}, err
  	}
  
  	diff := absDuration(time.Since(time.Unix(timestamp, 0)))
  	if diff > 5*time.Minute {
  		return SecretsVerifier{}, ErrExpiredTimestamp
  	}
  
  	return sv, err
  }
docs: // NewSecretsVerifier returns a SecretsVerifier object in exchange for an http.Header object and signing secret