Apache Reference: mod_auth_dbm

mod_auth_dbm - User Authentication by User Name/Password (UNIX NDBM)
Since Apache 1.0, src/modules/standard/mod_auth_dbm.c
Rob McCool, Robert S. Thau, Dirk van Gulik (1996)

mod_auth_dbm is a variant of mod_auth that provides the same functionality, but uses a standard UNIX NDBM hash file instead of a flat-file database. The advantage is a magnitude-better performance in the lookups (performed for every request) --- especially important consideration when the user community is very large. An NDBM library is provided by most all UNIX platforms.

Directives:

AuthDBMAuthoritative	AuthDBMGroupFile
AuthDBMUserFile