rustls-graviola support

[flyingmutant]

I have found these related issues/pull requests

Related: #4033.

Description

Graviola is a pure-Rust/asm crypto library made by the rustls author – with main goal being usable as rustls backend via rustls-graviola crate. We use Graviola with and without rustls and quite like it.

We currently use sqlx with tls-rustls-aws-lc-rs, which makes cross-compiling a pain, and are looking to migrate to rustls-graviola.

Prefered solution

tls-rustls-graviola feature (or a couple of features, with different root variants) looks like the simplest option (compared to e.g. #4033). If you are OK with this direction, I can work on a PR adding it to sqlx.

Is this a breaking change? Why or why not?

Not a breaking change – new optional feature.

[abonander]

The direction we're moving in is to just have a couple of TLS features for convenience, then anything outside of that you'll need to install a CryptoProvider in RusTLS yourself. Adding (and especially testing) a new TLS feature for each new crypto library someone might want to use is simply untenable.