code: func PeekAlgorithmAndIssuer(buf []byte) (Algorithm, string, error) {
  	var err error
  
  	// get algorithm
  	alg, err := PeekAlgorithm(buf)
  	if err != nil {
  		return NONE, "", err
  	}
  
  	// get issuer
  	issuer, err := PeekPayloadField(buf, "iss")
  	if err != nil {
  		return NONE, "", err
  	}
  
  	return alg, issuer, nil
  }
docs: // PeekAlgorithmAndIssuer extracts the signing algorithm listed in the "alg"
  // field and the issuer from the "iss" field of the serialized JWT buf's header
  // and payload, attempting to unmarshal alg to Algorithm and iss to a string.
  // An error will be returned if the Algorithm or Issuer fields are not
  // specified in the JWT header and payload, or are otherwise invalid.