Authorization with OAuth2

[binarin]

This snippet shows a few possible approaches for regularly updating secrets for SelectConnection's using OAuth2. It's not a finished work, but a point to start a discussion about this feature, and how/whether it'd be possible to support it properly in API, instead of every user hand-rolling their own implementation. (For reference, Java client already has it - https://www.rabbitmq.com/api-guide.html#oauth2-support).

Turns out implementing OAuth2-flow is not completely trivial. While fetching a new secret is easy (it's implemented here using requests_oauthlib , but to reduce dependencies this can be done in pure http), doing this regularly is a bit more complex task. I've tried the following 2 approaches:

• Doing a blocking http call in connection thread (see BlockingConnectionSecretRefresher). This is simple, but an OAuth2 http call takes ~0.3 second in my tests, which can be too much blocking.
• Running a separate thread (see ThreadedConnectionSecretRefresher). In this case it has no negative effect on processing speed, but introduces a lot of moving parts.

There is also a question of what to do with all other connection adapters. It looks like methods similar call_later/add_callback_threadsafe are universally available, but e.g. for aio/twisted adapters it should be possible to do the same using non-blocking http calls.

[binarin]

One way I envision is to sublclass PlainCredentials as OAuth2Credentials, and then do a special-case in every adapter, where a new thread for updates will be started automatically.