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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

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##           master     #222   +/-   ##
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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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[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://