In a large Linux only network how would you handle Authentication and User management?

After working with linux for years in small networks, I've started in a company that maintains large windows networks. I know you can cobble a linux host onto an Active Directory network but is there a tidy linux-y way of handling it if you didn't have to deal with Windows hosts. Purely hypothetical.

The closest equivalent to Active Directory for Linux is FreeIPA. FreeIPA is made by Redhat, and provides both LDAP and Kerberos based authentication to a Linux network...

FreeIPA is an integrated security information management solution combining Linux (Fedora), 389 Directory Server, MIT Kerberos, NTP, DNS, Dogtag (Certificate System). It consists of a web interface and command-line administration tools.

Bear in mind, FreeIPA is largely Redhat only, and would take a good bit of work to get up-and-running on Debian/Ubuntu/whatever...

http://freeipa.org/page/Main_Page

LDAP is an application protocol for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network.

Directory services may provide any organized set of records, often with a hierarchical structure, such as a corporate email directory. Similarly, a telephone directory is a list of subscribers with an address and a phone number.