how to make an authorization test using pytest without selenium

it is necessary to create an authorization test for the site yandex.ru, I can not even register there automatically. Using the library requests, i get something like:

USerID = 'XXX'
Pass = 'XXX'
url = 'https://yandex.ru'

session = rq.Session()
session.post(url, {
     'login_username': USerID,
     'login_password': Pass,
})
r = rq.get(url, auth = (USerID, Pass))