@Override
public void execute(CommandParser commandParser) throws IOException,
Pop3Exception {
if (session.getSessionState() != AUTHORIZATION_PASS_COMMAND_EXPECTED)
throw new IllegalSessionStateException();
String password = commandParser.parseSingleExtendedArgument();
LoginResult result =
loginSpecification.evaluatePlain(userCommand.user, password);
if (result.decision == LoginDecision.VALID) {
startTransaction(result.principal);