code: public boolean verify(String base64Signature, String content, String timestamp) throws Exception {
          return verify(base64Signature, content, timestamp, keyName);
      }
docs: Verifies the validity of the digital signature using stored key name.
  
  @param base64Signature The digital signature.
  @param content The authorization string to which the signature was applied.
  @param timestamp The timestamp of the digital signature.
  @return True if the signature is valid.
  @throws Exception Unspecified exception.