During the authentication phase, mod_authnz_ldap searches for an entry in the directory that matches the username that the HTTP client passes. If a single unique match is found, then mod_authnz_ldap attempts to bind to the directory server using the DN of the entry plus the password provided by the HTTP client. Because it does a search, then a bind, it is often referred to as the search/bind phase. Here are the steps taken during the search/bind phase.

1. Generate a search filter by combining the attribute and filter provided in the AuthLDAPURL directive with the username passed by the HTTP client.
2. Search the directory using the generated filter. If the search does not return exactly one entry, deny or decline access.
3. Fetch the distinguished name of the entry retrieved from the search and attempt to bind to the LDAP server using the DN and the password passed by the HTTP client. If the bind is unsuccessful, deny or decline access.

The following directives are used during the search/bind phase

During the authorization phase, mod_authnz_ldap attempts to determine if the user is authorized to access the resource. Many of these checks require mod_authnz_ldap to do a compare operation on the LDAP server. This is why this phase is often referred to as the compare phase. mod_authnz_ldap accepts the following Require directives to determine if the credentials are acceptable:

• Grant access if there is a require ldap-user directive, and the username in the directive matches the username passed by the client.
• Grant access if there is a require ldap-dn directive, and the DN in the directive matches the DN fetched from the LDAP directory.
• Grant access if there is a require ldap-group directive, and the DN fetched from the LDAP directory (or the username passed by the client) occurs in the LDAP group.
• Grant access if there is a require ldap-attribute directive, and the attribute fetched from the LDAP directory matches the given value.
• Grant access if there is a require ldap-filter directive, and the search filter successfully finds a single user object that matches the dn of the authenticated user.
• otherwise, deny or decline access

Other Require values may also be used which may require loading additional authorization modules.

• Grant access if there is a require valid-user directive. (requires mod_authz_user)
• Grant access if there is a require group directive, and mod_authz_groupfile has been loaded with the AuthGroupFile directive set.
• others...

mod_authnz_ldap uses the following directives during the compare phase:

If this directive exists, mod_authnz_ldap grants access to any user that has successfully authenticated during the search/bind phase. Requires that mod_authz_user be loaded and that the AuthzLDAPAuthoritative directive be set to off.

The require ldap-user directive specifies what usernames can access the resource. Once mod_authnz_ldap has retrieved a unique DN from the directory, it does an LDAP compare operation using the username specified in the require ldap-user to see if that username is part of the just-fetched LDAP entry. Multiple users can be granted access by putting multiple usernames on the line, separated with spaces. If a username has a space in it, then it must be surrounded with double quotes. Multiple users can also be granted access by using multiple require ldap-user directives, with one user per line. For example, with a AuthLDAPURL of ldap://ldap/o=Airius?cn (i.e., cn is used for searches), the following require directives could be used to restrict access:

Because of the way that mod_authnz_ldap handles this directive, Barbara Jenson could sign on as Barbara Jenson, Babs Jenson or any other cn that she has in her LDAP entry. Only the single require ldap-user line is needed to support all values of the attribute in the user's entry.

If the uid attribute was used instead of the cn attribute in the URL above, the above three lines could be condensed to

This directive specifies an LDAP group whose members are allowed access. It takes the distinguished name of the LDAP group. Note: Do not surround the group name with quotes. For example, assume that the following entry existed in the LDAP directory:

The following directive would grant access to both Fred and Barbara:

Behavior of this directive is modified by the AuthLDAPGroupAttribute and AuthLDAPGroupAttributeIsDN directives.

The require ldap-dn directive allows the administrator to grant access based on distinguished names. It specifies a DN that must match for access to be granted. If the distinguished name that was retrieved from the directory server matches the distinguished name in the require ldap-dn, then authorization is granted. Note: do not surround the distinguished name with quotes.

The following directive would grant access to a specific DN:

Behavior of this directive is modified by the AuthLDAPCompareDNOnServer directive.

The require ldap-attribute directive allows the administrator to grant access based on attributes of the authenticated user in the LDAP directory. If the attribute in the directory matches the value given in the configuration, access is granted.

The following directive would grant access to anyone with the attribute employeeType = active

Multiple attribute/value pairs can be specified on the same line separated by spaces or they can be specified in multiple require ldap-attribute directives. The effect of listing multiple attribute/values pairs is an OR operation. Access will be granted if any of the listed attribute values match the value of the corresponding attribute in the user object. If the value of the attribute contains a space, only the value must be within double quotes.

The following directive would grant access to anyone with the city attribute equal to "San Jose" or status equal to "Active"

The require ldap-filter directive allows the administrator to grant access based on a complex LDAP search filter. If the dn returned by the filter search matches the authenticated user dn, access is granted.

The following directive would grant access to anyone having a cell phone and is in the marketing department

The difference between the require ldap-filter directive and the require ldap-attribute directive is that ldap-filter performs a search operation on the LDAP directory using the specified search filter rather than a simple attribute comparison. If a simple attribute comparison is all that is required, the comparison operation performed by ldap-attribute will be faster than the search operation used by ldap-filter especially within a large directory.

FrontPage restricts access to a web by adding the require valid-user directive to the .htaccess files. The require valid-user directive will succeed for any user who is valid as far as LDAP is concerned. This means that anybody who has an entry in the LDAP directory is considered a valid user, whereas FrontPage considers only those people in the local user file to be valid. By substituting the ldap-group with group file authorization, Apache is allowed to consult the local user file (which is managed by FrontPage) - instead of LDAP - when handling authorizing the user.

Once directives have been added as specified above, FrontPage users will be able to perform all management operations from the FrontPage client.

• When choosing the LDAP URL, the attribute to use for authentication should be something that will also be valid for putting into a mod_authn_file user file. The user ID is ideal for this.
• When adding users via FrontPage, FrontPage administrators should choose usernames that already exist in the LDAP directory (for obvious reasons). Also, the password that the administrator enters into the form is ignored, since Apache will actually be authenticating against the password in the LDAP database, and not against the password in the local user file. This could cause confusion for web administrators.
• Apache must be compiled with mod_auth_basic, mod_authn_file and mod_authz_groupfile in order to use FrontPage support. This is because Apache will still use the mod_authz_groupfile group file for determine the extent of a user's access to the FrontPage web.
• The directives must be put in the .htaccess files. Attempting to put them inside Location or Directory directives won't work. This is because mod_authnz_ldap has to be able to grab the AuthGroupFile directive that is found in FrontPage .htaccess files so that it knows where to look for the valid user list. If the mod_authnz_ldap directives aren't in the same .htaccess file as the FrontPage directives, then the hack won't work, because mod_authnz_ldap will never get a chance to process the .htaccess file, and won't be able to find the FrontPage-managed user file.