I found a way to do it !
Thanks to this post on the opposite problem
I just added two parameters to my boot line in grub.cfg
It is now fully automated and not asking for any question.
You need to specify a password hash format instead of Cleartext-Password, and
You need to set auth_goodpass and auth_badpass to 'no' to prevent logging passwords.
Specifying a hash format
As described in the rlm_pap man page, there are a number of password hash settings that can be used instead of Cleartext-Password. Let us take a simple example,...