code: func ParsePrivateKeyPEM(keyPEM []byte) (key crypto.Signer, err error) {
  	return ParsePrivateKeyPEMWithPassword(keyPEM, nil)
  }
docs: // ParsePrivateKeyPEM parses and returns a PEM-encoded private
  // key. The private key may be either an unencrypted PKCS#8, PKCS#1,
  // or elliptic private key.