Add support for proxy-authorization header

[gabihodoroaga]

Fixes #346

[bshaffer]

This is great! We do need tests for this though. If you're able to add them, great! Otherwise I'll try to find time to write some.

[gabihodoroaga]

Thank you for review.
I implemented the changes.
I added unit tests. I skipped the tests related to the caching because this part is covered by the AuthTokenMiddlewareTest

[bshaffer]

This looks amazing! Thank you so much for adding the tests!

[bshaffer]

Congrats @gabihodoroaga for the Google Cloud PHP contribution of the year award :)

[gabihodoroaga]

Thank you ***@***.*** *I'm more than happy to know that this will help others in the future.

…

On Fri, Jun 25, 2021 at 9:41 PM Brent Shaffer ***@***.***> wrote: Congrats @gabihodoroaga <https://github.com/gabihodoroaga> for the Google Cloud PHP contribution of the year award :) — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#347 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABLI5TIBILBSGSN34OCLH3TTUTLXXANCNFSM47CO6LKA> .

[jhanley-com]

I was testing the Proxy-Authorization header yesterday (2021-08-17) and it does not work. I wrote up some details on Stack Overflow: https://stackoverflow.com/a/59297859/8016720 I would love feedback on a solution. I used both the CLI curl and the example in the PHP SDK: aaf2363