Added active scanner for the JWT "None" Exploit

[wg4568]

I wrote an active scanner rule to detect an exploit that arises from using poorly implemented JWT.

More info: https://www.sjoerdlangkemper.nl/2016/09/28/attacking-jwt-authentication/

[kingthorin]

Thanks for the contribution!

Edit: If you could address the two LGTM items as well that'd be wonderful (they're simple, just two lines missing var keyword).

[kingthorin]

@wg4568 do you plan to address the remaining comment?

[kingthorin]

@wg4568 do you plan to address the remaining comment?

[kingthorin]

Thanks

[thc202]

Thanks!