code: func getCertificate(file string) []byte {
  	derBytes, err := ioutil.ReadFile(file)
  	if err != nil {
  		fmt.Println(err)
  		return nil
  	}
  	// decode pem
  	block, _ := pem.Decode(derBytes)
  	if block != nil {
  		derBytes = block.Bytes
  	}
  	return derBytes
  }
docs: // getCertificate reads a single certificate from disk