I couldn’t login to Application Designer today for some reason. I kept getting an “Invalid User ID and password for signon.” error despite my credentials being correct.
It turned out that adding the EOPP_USER and PAPP_USER roles fixed the issue:
1: Navigate to the user’s profile (PeopleTools > Security > User Profiles > User Profiles)
2: Enter the user’s ID and press search
3: Select “Roles” from the top row of tabs
4: Add the “EOPP_USER” and “PAPP_USER” roles
5: Press save