test(io): move authentication related tests to test_auth.py

The `test_io.py` module is too bloated (2100+ lines). To
logically group related tests, as a first step, this commit
separates authentication related IO tests into `test_auth.py`
module.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

Author: taimoorzaeem