add option to load the private_key_password from a file

[ottigeda]

[alandekok]

It's not clear why this is useful? There isn't a lot of difference between the password being in a FreeRADIUS configuration file, or being in a different file on disk.

What's the use-case here? Is this security? Or simplicity, or...??

i.e. I can see that the patch does something, but it would be good to have an explanation as to why the patch is needed.

[ottigeda]

I use freeradius together with stepca certificate authority. Since stepca supports password stored in files, and we already use stepca that way, this patch would remove the need to have the password stored in multiple files. For me this is more the practical point of view, not so much security.