code: func LoadCertificateECDSA(certPath string) (*x509.Certificate, error) {
  	var cert *x509.Certificate
  	var err error
  
  	walkFunc := func(path string, info os.FileInfo, err error) error {
  		if strings.HasSuffix(path, ".pem") {
  			rawCert, err := ioutil.ReadFile(path)
  			if err != nil {
  				return err
  			}
  			block, _ := pem.Decode(rawCert)
  			cert, err = utils.DERToX509Certificate(block.Bytes)
  		}
  		return nil
  	}
  
  	err = filepath.Walk(certPath, walkFunc)
  	if err != nil {
  		return nil, err
  	}
  
  	return cert, err
  }
docs: // LoadCertificateECDSA load a ecdsa cert from a file in cert path