Remove openssl dependency - use Rustls for acme / letsencrypt

[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've had some issues with openssl as a dependency. It makes compiling harder, and i've had that binaries didn't run because of OpenSSL version mismatches. Not fun.

Options:

Fix current implementation acme_lib

acme_lib works fine, but it has a bunch of dependencies on OpenSSL for crypto stuff. This could be fixed, with ring for example. But it's not easy - lots of PEM dependencies, which ring doesnt support (see issue in acme-lib)

rustls-acme

• easy to understand API
• still maintained

async-acme

• Lots of options (rustls / tokio) that minimize deps issues
• No maintenence in a year

acme-micro

Uses openssl, so no

instant_acme (my favorite atm)

• Uses rustls and ring (which I use, too)
• Actively maintained
• No HTTP01 support as of now, but is being worked on

(current implementation)

I made the https and https_init optional features. Not a real solution!

Custom implementation

Poem has a custom implementation

future-io-utils also

• 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.