This function will delegate determining if we have the correct username and
password to authorize a user. The return value will be added to the request
with the keyword of :identity. We will accept either a valid username or
valid user email in the username field. It is a little strange but to adhere
to legacy basic auth api of using username:password we have to make the
field do double duty.

Use the basic-auth function defined in this file as the authentication
function for the http-basic-backend

The username and email values are stored in-memory for this reference implementation.