Authentication

[AzureMarker]

Create a way to authenticate the API user. Most endpoints will be protected. The authentication will be session-based like the current PHP web interface. The security can potentially be tighter as well, but that may be improved after the initial authentication is implemented.

This story will be developed alongside web.
Corresponding issue: pi-hole/web#10

This can be done by creating a Request Guard.

An example of a session-based authentication is found in one of Rocket's tests.