Currently if the authentication callback returns `FALSE` the utils
function handle this as scenario as no credentials provided (returns
`AUTH_NO_CREDENTIALS)`.
This PR introduces a new `auth_status` called `AUTH_CANCELLED` that is
returned if the authentication callback returns `FALSE`. If the callback
returns `TRUE` and username or password are empty the util function will
continue to return `AUTH_NO_CREDENTIALS`.
THe PR also fixes some incorrect returns in RPC over HTTP gateway code.
1f903f80a5