FCM API Credential refresh mechanism doesn't support HTTP proxies and blocks the event loop

[reivilibre]

title says it all: it doesn't look like we support HTTP proxies here and given no await I suspect this also blocks the event loop:

sygnal/sygnal/gcmpushkin.py

Line 480 in c025ac1

credentials.refresh(request)

[reivilibre]

aiohttp supports proxies: https://docs.aiohttp.org/en/stable/client_advanced.html#proxy-support

as does HTTPX, which sounds like it could be the next big thing in Python, or maybe that's just some inflated hype — would need consideration: https://www.python-httpx.org/

(Either of these would probably be preferable to us hacking our own CONNECT proxy support into Twisted and asyncio using two similar but different bits of code. Realistically it doesn't make that much sense for us to be using Twisted in Sygnal anymore)

[MatMaul]

The google-auth lib seems to support a custom urllib3 pool: https://googleapis.dev/python/google-auth/latest/user-guide.html#urllib3

To my understanding we can replace an urllib3 PoolManager by a ProxyManager: https://urllib3.readthedocs.io/en/stable/advanced-usage.html#proxies

I guess it would be the straightest way to support a proxy here, what do you think ?

[MatMaul]

Oh urllib3 is blocking, but it seems we are using the requests backend for now, which is also blocking, hence the fact that there is no await I think.

We can also customize the requests Session, and use a proxy there: https://docs.python-requests.org/en/latest/user/advanced/#proxies

[MatMaul]

google-auth has an aiohttp backend even if it seems undocumented.

And it seems that it can support a custom Session which easily supports a proxy, so we may have an easy-ish async way forward.

[MatMaul]

To be clear so we don't double the work, we need proxy support on our deploy so I am currently working on that, I should be able to send a PR this week.