Auto-Closing window for ImplicitGrantAuthController

[jholzer]

In case we have multiple authentications (e.g. after token timeout) there may be several open windows caused by authentication redirect.
With different response the web browser will close the window automatically,
In worst case (e.g. no javascript) the original message will be displayed.

[JohnnyCrazy]

I guess it's cool for a short string like this. In the future, let's consider adding such stuff to a html file and deliver this instead of sending a raw string.

Thanks! 👍