public boolean isValid() {
        return System.nanoTime() - lastFailure <= duration;
    }
Returns whether this authentication failure is recent enough that it
should still be tracked. This function will return false for
authentication failures that have not recurred for at least the duration
provided at construction time.

@return
    true if this authentication failure is recent enough that it should
    still be tracked, false otherwise.
extensions/guacamole-auth-ban/src/main/java/org/apache/guacamole/auth/ban/status/AuthenticationFailureStatus.java