Add support for UNIX sockets

[Koenvh1]

The idea is to use a local unix domain socket and authenticate via the local user (root by default, other users are configurable). This allows for the use of krillc without explicitly supplying a token.

The configuration looks like this:

unix_socket = "/tmp/krill.sock"
unix_users = { root = "admin", koen = "readonly" }

This allows for running krillc without KRILL_CLI_TOKEN:

koen@beta:~/Code/krill/target/debug$ ./krillc list
testca

[partim]

I feel like this is the point where we should start having separate HTTP client implementations for the client and server portions. So my suggestion would be to copy src/commons/httpclient.rs into a new src/cli/httpclient.rs and only modify that to be able to use Unix sockets.

Maybe it would be useful to then also create a HttpClient type and move the possible socket and possible token in there (this would also allow to have either a token or a socket). This way you don’t need to do splitting of the URL – I feel uneasy relying on the socket having a filename ending in .sock or else stuff breaking – but rather work with a http://localhost prefix.

[Koenvh1]

I'm fine with pulling the two clients apart, although I would rename them to avoid mixing them up. Not sure about whether a generic type would really work for this, though a type that contains the socket separately rather than parsing the URI over and over is something I can get behind.

I'm happy to hear what you suggest as URI scheme - keep unix://something/that/could/be/a/path and make every request to http://localhost/api/do/something?

[partim]

I would probably have two entirely separate implementations. The overlap is relatively small, the two use cases are quite different.

I would indeed keep the current scheme for configuration but translate that internally into an HTTP URI (I think the host portion doesn’t matter at all) and a correctly configure reqwest client.