use request cancellationtoken

[Poltuu]

It is very important to handle browser refresh/closing properly, and is pretty easy to do.
This can be done with a mvc filter + passing the cancellationtoken from top to bottom.

This is a massive API breaking change thus, as basically every XXXAsync API needs to be patched, but I believe is a very important change

[nfaugout-lucca]

SemVer + breaking change = Label v4 ;)

[rducom]

No need of a filter, MVC inject cancellation tokens in action method parameters

[Poltuu]

filter is not for token injection, but for proper handling of OperationCanceledException