CMS Made Simple Forums

I´m using cmsms 2.1.6 and Frontend Users 2.2.0.6 with "Builtin Authentication"

My problem:
I would like to set a timestamp in localStorage (with javascript) when a frontend user successfully logged in.
Can anyone help me to figure out if it is possible and where to put the code?

Inside FEU you can define a page for redirecting users after successful login.

Define such a page (not shown in menu) and add this javascript to this page