User running httpd2 must be in group 'shadow' and 'auth' (for ALT)
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=394097)

Enable modules:
 auth_basic
 authn_pam
 authz_user

Config:
<Directory "/local/www">
    AuthType Basic
    AuthName "Private Access"
    AuthBasicProvider pam
    Require valid-user
</Directory>


Details in http://mod-auth.sourceforge.net/docs/mod_authn_pam/