code: func ParseSelfSignedCertificatePEM(certPEM []byte) (*x509.Certificate, error) {
  	cert, err := ParseCertificatePEM(certPEM)
  	if err != nil {
  		return nil, err
  	}
  
  	if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
  		return nil, cferr.Wrap(cferr.CertificateError, cferr.VerifyFailed, err)
  	}
  	return cert, nil
  }
docs: // ParseSelfSignedCertificatePEM parses a PEM-encoded certificate and check if it is self-signed.