Provide Access-Control-Allow-Credentials support

[dnp1]

Hello,
I have a web application in angular that access multiple apis using cookies as credentials
The Browser refuses to send cookies if Access-Control-Allow-Credentials isn't setted.

Do you intent offer this support in this library?
If yes, I'll open a pull request.

[dbrgn]

Hi

It seems that I overlooked Access-Control-Allow-Credentials when implementing this chart.

A pull request is welcome, yes!