This week’s TechMail tip is Authentication caching with nscd which talks about how to keep authentication credentials cached for disconnected operations (i.e. if you auth against an LDAP server and it goes down or you take your laptop home).
It’s missing some bits tho, which the first comment noted. It doesn’t discuss PAM at all, which would be required for the actual authentication as all it does is essentially provide a cache of passwd/group, but not shadow (which I neglected to mention when I wrote the original tip).