Prohibition of work in several simultaneous sessions

The RestrictSessions procedure prohibits working in multiple sessions.

public class RestrictSessions implements Strategy {

    private final Logger logger = LoggerFactory.getLogger("com.identityblitz.idp.flow.dynamic");

    @Override public StrategyBeginState begin(final Context ctx) {
      List<String> methods = new ArrayList<String>(Arrays.asList(ctx.availableMethods()));
      if ("login".equals(ctx.prompt())){
        methods.remove("cls");
        return StrategyState.MORE(methods.toArray(new String[0]), true);
      } else {
        if(ctx.claims("subjectId") != null)
          return StrategyState.ENOUGH();
        else {
          methods.remove("cls");
          return StrategyState.MORE(methods.toArray(new String[0]));
        }
      }
    }

    @Override public StrategyState next(final Context ctx) {
      Integer reqFactor = (ctx.user() == null) ? null : ctx.user().requiredFactor();
      if(reqFactor == null || reqFactor == ctx.justCompletedFactor()) {
        return StrategyState.ENOUGH_BUILDER().singleSession(true).build();
      } else
        return StrategyState.MORE(new String[]{});
    }
}