The Nanoflow sign in action can be used to sign someone in, from a page where the user specifies the username & password in “normal” input textboxes. These should be within a dataview connected to a non-persistable entity with two attributes; UserName and Password. ← in other words; completely self-build custom sign in behavior.
Solution you could use is; use the default/userrole home page. Change this to call microflow and model your magic to check the token. after your magic, open the page of your liking as homepage
Not sure what use case is making you need to check the token, but here is one option to explore:
You can use after start-up microflow under Settings-Runtime. However, if you allow anonymous users, then this will be fired even before the user signs in
Also there is a widget "Signin Microflow” that could help in your case (https://marketplace.mendix.com/link/component/66443) not sure if it works in Mx9.
After login to a Mendix app the username entered in the login form is in $currentUser/Name. The password is stored as hash in Mendix, but is a hash of what was typed in the login form. If you need the values as entered in the login form (the page where the user does not have a Mendix session yet, except for anonymous users redirected from the index page), you can send the form values to Mendix by an ajax REST call from the login page with a little Javascipt code and store them connected to the account for later retrieval in a microflow after login.