code: public boolean validate(Signer signerToUse) throws CoseException {
          for (Signer r : signerList) {
              if (r == signerToUse) {
                  return r.validate(rgbProtected, rgbContent);
              }
          }
          
          throw new CoseException("Signer not found");
      }
docs: Validate the signature on a message for a specific signer.
  The signer is required to be one of the Signer objects attached to the message.
  The key must be attached to the signer before making this call.
  
  @param signerToUse which signer to validate with
  @return true if the message validates with the signer
  @throws CoseException Errors generated by the COSE module