[rust-server] no support for native CA certificate store

[bjgill]

Description

rust-server doesn't provide a simple method (or example) to create an HTTPS client/server that authenticates servers/clients against the system's native CA certificate store.

Instead, rust-server is designed so that you provide the path to a single CA certificate.

This means that using rust-server to talk to servers on the public web (e.g. Google) can be quite a pain.

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Steps to reproduce

Related issues/PRs

Found in #1199 (comment)

Suggest a fix/enhancement

Provide a variant of Client::try_new_https that uses the native CA certificate store.

Maybe we could have ca_certificate: CA, CA: Into<Option<Path>?

[kanekv]

@bjgill would it be easier to support reqwest as an option?

[bjgill]

It'd certainly be possible. Switching the HTTP client library seems likely to be quite painful, however.