Depends if you turn to third-party mods or not.

• mod_auth_mysql
• mod_auth_pgsql
• mod_auth_tds (for Sybase/MS SQL)
• mod_auth_oracle
• etc.

Of course, (and to keep things on topic for PerlMonks :)) you can always try something like Apache::AuthzDBI with mod_perl, or some custom perl script with mod_auth_external.

    --k.