async-tungstenite: Make TLS features optional

[felinira]

The included TLS features are only required for wss connections to the mailbox server which not required by the protocol and only really useful for wasm builds.

Closes #216

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 39.24%. Comparing base (6082d8b) to head (7366377).

Additional details and impacted files

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  Coverage   39.24%   39.24%           
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  Files          18       18           
  Lines        3088     3088           
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  Hits         1212     1212           
  Misses       1876     1876           

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[piegamesde]

Ideally I'd like to have the default rendezvous server listen to wss by default, but until that happens (it honestly won't anytime soon anyways) this is probably the right thing to do.

[felinira]

Either way we need a way to select the backend here. I would personally choose native TLS for example, to get rid of rustls and ring. I can make it a default feature instead.

wss support doesn't really give us much though, does it? What advantage do we have from connecting to a server via wss? From what I gathered the reason for wss support is mostly due to wasm requirements?

[meejah]

wss support doesn't really give us much though, does it?

Not really, it's already end-to-end encrypted in the protocol itself (and authenticated).

I believe at least part of the point of the default server being TCP-only is to prove this point (although I've not seen this written down anywhere by Brian).

[felinira]

I'll leave it out of default features for now. Cargo doesn't support target-specific default features so we can't auto-enable it on wasm either (wasm being the only place where it makes sense to both enable it by default, and native tls doesn't exist)

[meejah]

Yes, typically WASM will require wss://