Add function to use TLS when pushing to gateway

[Roymprog]

Closes #982

[csmarchbanks]

Rather than create a second function could we add another argument for verify_mode to tls_auth_handler?

[Roymprog]

We could, the reason I didn't do that was the name of the function. The name tls_auth_handler implies it does authentication. The function becomes confusing if you allow to not provide your own TLS certificate and only use it to verify the certificate of the server.

I'd propose keeping one function called tls_handler, but that would be a breaking change.

[csmarchbanks]

Ahh right, that makes sense, and I think having an auth specific handler is nice.

What would this function provide over just using an https scheme in push_to_gateway? I guess the use case is for if you need to specify the cafile and verify mode?

[Roymprog]

What would this function provide over just using an https scheme in push_to_gateway? I guess the use case is for if you need to specify the cafile and verify mode?

That can be done. It's how I'm doing it right now. If you want to go that route, it would be better to make _make_handler a public function. Otherwise users would need to copy the boilerplate code from that function to create the handler. HTTPShandler cannot be passed to push_to_gateway directly, as it expects a callable (which HTTPShandler) is not.

[csmarchbanks]

I might be missing something as well, but perhaps this is a bug? I believe push_to_gateway is supposed to just work for https, and you are saying that you need to pass a custom handler to make it work? I wonder if we just need to use the scheme of the url to choose HTTP vs HTTPS in default_handler?

[Roymprog]

The default_handler works with HTTPS by default. The issue I have is that I need to use a custom SSL context because I need to load a custom trust location. I cannot do that through the default_handler. So, it's unnecessary to specify the scheme.
What would be nice in that case is to have an optional SSL context argument for the default_handler.

[csmarchbanks]

That makes sense, thank you.

Adding a custom context to default_handler as you suggest seems like it could be a good, and more general solution? That way users could customize the context as they need without us supporting every argument.

I am still thinking about it some and happy to hear other opinions, or advantages/disadvantages of that approach to what you have here. My main concern with this PR is that having two tls related handlers will be confusing.