I've just pushed a patch to KWallet5 allowing you to have your wallet unlocked automagically during login. This patch was originally done by Alex Fiestas for KWallet4, so all credits and free beers go to him; I've merely just forward-ported it.
You'll also require kde:kwallet-pam repo and pass "-DKWALLET5=1" to cmake. This will generate pam_kwallet5.so which then can be coinstalled with the same module for KWallet4 (plus it also enables some ifdef'd code inside the module). If you're still using some KDE4/Qt4 software which is using KWallet4, you will require both modules present.
How to set up kwallet-pam can be found over at Luca's blog (though he said he'll update it for KWallet5 later, so you may want to wait a bit :).