Support Basic Auth with Fixed Credentials

[sonatsuer]

When hit by a request with Basic authentication in its header, Blaze should check the credentials against the values of the following environment variables.

BASICAUTH_USER=<user, most likely 'root'>
BASICAUTH_PASSWORD=<password, ideally generated>

The credentials --or at least the password-- is likely to change on every restart so Blaze can read them on startup and keep them in memory. There is no need to persist.