Rustls support

[mdecimus]

Describe the solution you'd like
Would like to have the possibility of using rustls as a crypto backend instead of OpenSSL.

[akrantz01]

I'd love to have ring, the backend for rustls, be the default crypto backend. In fact, it was my original goal to avoid using OpenSSL at all. However, it is currently impossible to do as ring does not provide a way to export the components of private keys.

Another less blocking issue is that ring does not support generating RSA keypairs. Until that issue is fixed, I think the simplest workaround would be to use the rsa crate to generate the keys.

[mdecimus]

Perhaps you could check how rustls-acme implemented ACME using ring. They are not using the rsa crate to generate key pairs, but since I haven't read the specification, perhaps it is needed to support DNS-01 or HTTP-01 which are not supported by rustls-acme (they only support TLS-ALPN-01).

[akrantz01]

As far as I can tell, rustls-acme doesn't support using RSA keypairs for requesting certificates (see Account::generate_key_pair and Account::create_with_keypair).

Regardless, the main blocker is still not having a way to export private key components. There's probably a workaround somewhere, to get it working with ring, but I don't have time at the moment to explore that.