Feature request: use libpam for luci web login

[ghost]

What would you like to see in luci?

currently luci reads /etc/shadow to check password, instead of using libpam like other linux distros (debain/centos/etc), even if libpam is installed and configured.

this can also be a security risk as it allows one to by-pass MFA authentication for openssh

[systemcrash]

You're welcome to submit a PR