code: func tlsConfigKey(c *Config) (string, error) {
  	// Make sure ca/key/cert content is loaded
  	if err := loadTLSFiles(c); err != nil {
  		return "", err
  	}
  	// Only include the things that actually affect the tls.Config
  	return fmt.Sprintf("%v/%x/%x/%x", c.TLS.Insecure, c.TLS.CAData, c.TLS.CertData, c.TLS.KeyData), nil
  }
docs: // tlsConfigKey returns a unique key for tls.Config objects returned from TLSConfigFor