Setting the AuthAuthoritative directive explicitly to
'off' allows for both authentication and authorization to
be passed on to lower level modules (as defined in the
Configuration and modules.c files) if there is
no userID or rule matching the
supplied userID. If there is a userID and/or rule specified; the
usual password and access checks will be applied and a failure will
give an Authorization Required reply.
So if a userID appears in the database of more than one module; or if a valid require directive applies to more than one module; then the first module will verify the credentials; and no access is passed on; regardless of the AuthAuthoritative setting.
A common use for this is in conjunction with one of the
database modules; such as
mod_auth_db.c,
mod_auth_dbm.c, mod_auth_msql.c, and mod_auth_anon.c. These
modules supply the bulk of the user credential checking; but a few
(administrator) related accesses fall through to a lower level with
a well protected AuthUserFile.
Default: By default; control is not passed on; and an unknown userID or rule will result in an Authorization Required reply. Not setting it thus keeps the system secure; and forces an NCSA compliant behaviour.
Security: Do consider the implications of allowing a user to allow fall-through in his .htaccess file; and verify that this is really what you want; Generally it is easier to just secure a single .htpasswd file, than it is to secure a database such as mSQL. Make sure that the AuthUserFile is stored outside the document tree of the web-server; do not put it in the directory that it protects. Otherwise, clients will be able to download the AuthUserFile.
See also AuthName, AuthType and AuthGroupFile.