I've noticed that most apps don't show predictive text suggestions on keypads on login screens. Why is that? Is there some security issue around entering password?
If you are unable to verify that the person accessing the login screen is a trusted user, then displaying predictive text on a username field leads to a very high risk of security breaches because only the password field needs to be determined by the hacker.
If you are able to verify that the person accessing the login screen is a trusted user, then displaying predictive text on a user name field provides some degree of convenience especially if there are multiple people that are likely to access the screen, or if a single person has multiple usernames/accounts that will make input simpler.
I don't think there should ever be any predictive text on password fields, but perhaps asking this question on security stackexchange might help you to answer some of the technical and practical aspects of this question.
Predictive searching would certainly be a security problem. Anyone borrowing your computer could quickly find most of your passwords.
However, 'remember password' is a nice feature from a user perspective that browsers like Chrome offer.
The problem is that lots of sites block this by setting the
autocomplete attribute on the password field to
They do this in the name of 'security' but it's an incredibly annoying feature for the user.
And, ultimately, it can make the site less secure as the user is tired of having to manually enter a password every time and may simply choose a shorter, easier-to-remember password in response.