Remove openssl dependency - use Rustls

[joepio]

I think (although I'm not entirely sure) that OpenSSL is the only runtime dependency of atomic-server. It's required only for the HTTPS setup process, which is currently done using acme_lib. ~~I could use rustls-acme for this~~, no use async-acme.

Also, I could make the https setup process an optional feature, which seems a bit easier.

I don't think this issue should be a priority, as most runtimes already have OpenSSL - or they can use my docker image.

• [x] Make HTTPS optional, allows for non-OpenSSL required builds
• [ ] Use Rustls for initialization (rustls-acme / async-acme)

[jonassmedegaard]

rustls-acme uses async-std which is currently used very little (see #366). Maybe a better option is async-acme?

[jonassmedegaard]

rustls-acme also causes duplicate older branches of ureqand rustls to be pulled in, because it depends on unstable 0.x APIs and haven't been updated for some time.

[joepio]

async-acme looks even better indeed!

[jonassmedegaard]

until this issue is solved, it might make sense to consider acme-micro which seems a (somewhat) more actively maintained fork of acme_lib.

[joepio]

This issue just got a bit more important. My own CI pipeline broke because of openssl version mismatch. I didn't know that could happen. It even makes running the docker container impossible.