action=clientlogin is supposed to be interactive, however our quick&dirty implementation just expects username, password and rememberMe parameters to be asked. If login error of missing params occurs, Pywikibot should interactively ask for them.
Find the clientlogin code in pywikibot/login.py and pywikibot/data/api.py, add a check if login error of missing params occurs and then interactively ask for the missing stuff. https://www.mediawiki.org/wiki/API:Login explains the interactiveness of the login process to the detail.
Also if login error occurs, there should be a check if login is even allowed to avoid T249403