code: func initCertPool() *x509.CertPool {
  	if customCACertsPath := os.Getenv(caCertificatesEnvVar); customCACertsPath != "" {
  		customCAs, err := ioutil.ReadFile(customCACertsPath)
  		if err != nil {
  			panic(fmt.Sprintf("error reading %s=%q: %v",
  				caCertificatesEnvVar, customCACertsPath, err))
  		}
  		certPool := x509.NewCertPool()
  		if ok := certPool.AppendCertsFromPEM(customCAs); !ok {
  			panic(fmt.Sprintf("error creating x509 cert pool from %s=%q: %v",
  				caCertificatesEnvVar, customCACertsPath, err))
  		}
  		return certPool
  	}
  	return nil
  }
docs: // initCertPool creates a *x509.CertPool populated with the PEM certificates
  // found in the filepath specified in the caCertificatesEnvVar OS environment
  // variable. If the caCertificatesEnvVar is not set then initCertPool will
  // return nil. If there is an error creating a *x509.CertPool from the provided
  // caCertificatesEnvVar value then initCertPool will panic.