This change replaces OpenSSL with rustls and also the manually curated
CA certs file with webpki-roots (effectively the same thing, but as a
crate).
Generally speaking the design of the network stack is the same. Changes:
- Code around certificate overrides needed to be refactored to work with
rustls so the various thread-safe list of certificates is refactored
into `CertificateErrorOverrideManager`
- hyper-rustls takes care of setting ALPN protocols for HTTP requests,
so for WebSockets this is moved to the WebSocket code.
- The safe set of cypher suites is chosen, which seem to correspond to
the "Modern" configuration from [1]. This can be adjusted later.
- Instead of passing a string of PEM CA certificates around, an enum is
used that includes parsed Certificates (or the default which reads
them from webpki-roots).
- Code for starting up an SSL server for testing is cleaned up a little,
due to the fact that the certificates need to be overriden explicitly
now. This is due to the fact that the `webpki` crate is more stringent
with self-signed certificates than SSL (CA certificates cannot used as
end-entity certificates). [2]
1. https://wiki.mozilla.org/Security/Server_Side_TLS
2. https://github.com/briansmith/webpki/issues/114Fixes#7888.
Fixes#13749.
Fixes#26835.
Fixes#29291.
