If you are sure that you want it, you could do it the same way you do it on Ubuntu. Ubuntu uses GNOME Display Manager for login screen. It passes the password to a PAM module that unlocks the default keyring for you. The PAM module seems to be already installed. To achieve what you want, you could install GDM. Some of it dependencies recommend a lot of x11 packages which I do not see necessary. So, here is what worked for me.
$ sudo apt install gdm3 --no-install-recommends
If you reboot now, you will see GDM for a moment, but it will be quickly overtaken by the usual Phosh login screen. Disabling Phosh service helped.
$ sudo systemctl disable phosh
Now, when you reboot, you can login with GDM. If you cannot, fold down the keyboard and touch the 
icon hiding in the bottom right corner under the screen keyboard. Select Phosh session instead or X11.
When you login via GDM, the default keyring should be unlocked automatically.