* Auth: Do not search for the user twice
Previously `initContextWithBasicAuth` did not use `LoginUserQuery`, doing
`GetUserByLoginQuery` only i.e. looking user in DB only, things changed when
this function started to check LDAP provider via `LoginUserQuery` (#6940),
however, this request was placed after `GetUserByLoginQuery`, so we first
looking in DB then in the LDAP - if LDAP user hasn't logged in we will
not find it in DB, so `LoginUserQuery` will never be reached.
`LoginUserQuery` request already performs `GetUserByLoginQuery`
request in correct sequence. So we can just remove redundant request.
* Correct sequence execution during authentification &
introduce tests for it
* Move basic auth tests to separate test file, since main test file already
pretty large
* Introduce `testing.go` for the middleware module
* Remove redundant test helper function
* Make handler names more explicit
Ref 5777f65d
Fixes #18329
* Auth: address review comment
