Feature request: Feature for using vendored OpenSSL

[VorpalBlade]

You have a feature to use rusttls. Unfortunately that is not supported on all architectures of Linux that I target (RISCV for example) due to ring not supporting those platforms.

It would however be nice if there was a feature to use a vendored version of OpenSSL, as I have had problems with matching the correct version of OpenSSL between CI builds and actual target systems. It seems using the system library on Linux for OpenSSL is a mess.

I believe this corresponds to the native-tls-vendored feature of reqwest.

[VorpalBlade]

It would also be nice for the default-tls to be a proper option, rather than hidden in default. Currently it is not possible from what I can tell to use self_update with default-features = false and then optionally re-enable native TLS support using something like: updater-tls-native = ["updater/default"] (this creates a cargo error).