* Add more specific error message when request body digest is invalid
This may help other implementors debug their implementation.
* Relax Host parameter requirement to GET requests
The only POST requests processed by Mastodon need objects/actors (including
their host) to be explicitly mentioned in the request's body, so replaying
a legitimate request to another host should not be a security issue.
* Support Digest headers using multiple algorithms or lowercase alogirthm names
