Support using rustls with AWS-LC crypto library
The arti, arti-client and tor-rtcompat crates now have rustls-ring
and
rustls-aws-lc
features that enable using rustls with the specified
crypto backend. The rustls
feature is now an alias for rustls-ring
for backwards-compatibility.
If both features are used, it defaults to using ring, which allows the features to be additive.
This doesn't address the licensing issue with ring because AWS-LC also contains code under the old OpenSSL license. But it might be advantageous for other reasons.
Fixes #1378.