protected DigitallySigned parseSignature(InputStream input) throws IOException {
   DigitallySigned signature = DigitallySigned.parse(context, input);
   SignatureAndHashAlgorithm signatureAlgorithm = signature.getAlgorithm();
   if (signatureAlgorithm != null) {
     TlsUtils.verifySupportedSignatureAlgorithm(supportedSignatureAlgorithms, signatureAlgorithm);
   }
   return signature;
 }