@Override
  public boolean validate(final BlockHeader header, final BlockHeader parent) {
    final long nonce = header.getNonce();
    if (!CliqueBlockInterface.isValidVoteValue(nonce)) {
      LOG.info("Invalid block header: Nonce value ({}) is neither auth or drop.", nonce);
      return false;
    }
    return true;
  }
Responsible for ensuring the nonce is either auth or drop.

@param header the block header to validate
@param parent the block header corresponding to the parent of the header being validated.
@return true if the nonce in the header is a valid validator vote value.
consensus/clique/src/main/java/org/hyperledger/besu/consensus/clique/headervalidationrules/VoteValidationRule.java