HTTP authentication

[imobachgs]

The goal of this PR is to add HTTP authentication support using a JSON Web Token.

Authentication

Once the server is running, you can authenticate using cURL:

$ curl http://localhost:3000/authenticate \
    -H "Content-Type: application/json" \
    -d '{"password": "your-password"}' 
{"token":"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE3MDg1MTA5MzB9.3HmKAC5u4H_FigMqEa9e74OFAq40UldjlaExrOGqE0U"}⏎

Now, you need to include the token on the subsequent calls:

$ curl -X GET http://localhost:3000/protected \
      -H "Accept: application/json" \
      -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE3MDg1MTA5MzB9.3HmKAC5u4H_FigMqEa9e74OFAq40UldjlaExrOGqE0U"

Introducing a configuration mechanism

This PR adds a new (and experimental) configuration mechanism that searches in /usr/etc/agama.d/ and /etc/agama.d/ for YAML/JSON-based configuration files. For convenience, it reads ./agama-dbus-server/share/server.yaml too. You can find a configuration example in the repository.

Additional notes

A temporary WEB-SERVER.md file contains some tips about working with this web server.

[coveralls]

coverage: 73.918% (-0.02%) from 73.938%
when pulling f10ffd1 on http-auth
into 0a2e7b6 on master.

[lslezak]

Just some PAM questions.

[lslezak]

I'm still learning Rust but this looks reasonable. 😃