code: func CanReadCertAndKey(certPath, keyPath string) (bool, error) {
  	certReadable := canReadFile(certPath)
  	keyReadable := canReadFile(keyPath)
  
  	if certReadable == false && keyReadable == false {
  		return false, nil
  	}
  
  	if certReadable == false {
  		return false, fmt.Errorf("error reading %s, certificate and key must be supplied as a pair", certPath)
  	}
  
  	if keyReadable == false {
  		return false, fmt.Errorf("error reading %s, certificate and key must be supplied as a pair", keyPath)
  	}
  
  	return true, nil
  }
docs: // CanReadCertAndKey returns true if the certificate and key files already exists,
  // otherwise returns false. If lost one of cert and key, returns error.