Play Framework how to purposely delay a response - amazon-web-services

Question

We have a Play app, currently using version 2.6. We are trying to prevent dictionary attacks against our login by delaying a "failed login" message back to our users when they provide a failed password. We currently hash and salt and have all the best practices, but we are not sure if we are delaying correctly. So we have in our Controller:
public Result login() { return ok(loginHtml) }
and we have a:
public Result loginAction()
{
// Check for user in database
User user = User.find.query()...
// Was the user found?
if (user == null) {
// Wrong password! Delay and redirect
Thread.sleep(10000); <<-- how do delay correctly?
return redirect(routes.Controller.login())
}
// User is not null, so all good!
...
}
We are not sure if Thread.sleep(10000) is the best way to delay a response since this might hang other requests that come in, or use too many thread from the default pool. We have noticed that under 80+ hits per second the Play Framework does not route our HTTP calls to the Routes. That is, if we receive a HTTP POST request, our app will not even send that request to the Controller until 20+ seconds later, HOWEVER, in the SAME time period if we get a HTTP GET request, our app will process that GET instantly!
Currently we have 300 threads as the min/max in our Akka settings for the default fork pool. Any insights would be appreciated. We run a t2.xlarge AWS EC2 instance running Ubuntu.
Thank you.

Answer 1

Thread.sleep causes current thread blocking, please, try to avoid using it in production code as much as possible.
What you need to use, is CompletionStage / CompletableFuture or any abstraction for deeling with async programming and asynchronous action.
Please, take a look for more details about asynchronios actions: https://www.playframework.com/documentation/2.8.x/JavaAsync
In your case solution would look like something too (excuse me, please, this might have mistakes - I'm Scala engineer primary):
import play.libs.concurrent.HttpExecutionContext;
import play.mvc.*;
import javax.inject.Inject;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
public class LoginController extends Controller {
private HttpExecutionContext httpExecutionContext;
// Create and inject separate ScheduledExecutorService
private ScheduledExecutorService executor;
#Inject
public LoginController(HttpExecutionContext ec,
ScheduledExecutorService executor) {
this.httpExecutionContext = ec;
this.executor = executor;
}
public CompletionStage<Result> loginAction() {
User user = User.find.query()...
if (user == null) {
return executor.schedule(() -> {redirect(routes.Controller.login());}, 10, TimeUnit.SECONDS);
} else {
// return another response
}
}
}
Hope this helps!

Answer 2

I don't like this approach at all. This hogs threads for no reason and can probably cause your entire system to lock up if someone finds out you are doing this and they have malicious ideas. Let me propose a better approach:
In the User table store a nullable LocalDateTime of the last login attempt time.
When you fetch the user from the DB check the last attempt time (compare to LocalDateTime.now()), if 10 secs have passed since last attempt perform the password comparison.
If passwords don't match store the last attempt time as now.
This can also be handled gracefully on the front end if you provide good error responses.
EDIT: If you want to delay login attempts NOT based on the user, you could create an attempt table and store last attempt by IP address.
If you really want to do your way which I don't recommend you need to read up on this first: https://www.playframework.com/documentation/2.8.x/ThreadPools