Apache HTTP Server Version 2.0
Apache Module mod_auth_ldap
|Description:||Allows an LDAP directory to be used to store the database for HTTP Basic authentication.|
|Compatibility:||Available in version 2.0.41 and later|
mod_auth_ldap supports the following features:
- Known to support the OpenLDAP SDK (both 1.x and 2.x), Novell LDAP SDK and the iPlanet (Netscape) SDK.
- Complex authorization policies can be implemented by representing the policy with LDAP filters.
- Support for Microsoft FrontPage allows FrontPage users to control access to their webs, while retaining LDAP for user authentication.
- Uses extensive caching of LDAP operations via mod_ldap.
- Support for LDAP over SSL (requires the Netscape SDK) or TLS (requires the OpenLDAP 2.x SDK or Novell LDAP SDK).
There are two phases in granting access to a user. The first
phase is authentication, in which
verifies that the user's credentials are valid. This also called
the search/bind phase. The second phase is
authorization, in which
if the authenticated user is allowed access to the resource in
question. This is also known as the compare
During the authentication phase,
searches for an entry in the directory that matches the username
that the HTTP client passes. If a single unique match is found,
mod_auth_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.
- Generate a search filter by combining the attribute and
filter provided in the
AuthLDAPURLdirective with the username passed by the HTTP client.
- Search the directory using the generated filter. If the search does not return exactly one entry, deny or decline access.
- 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
||Specifies the LDAP server, the base DN, the attribute to use in the search, as well as the extra search filter to use.|
||An optional DN to bind with during the search phase.|
||An optional password to bind with during the search phase.|
During the authorization phase,
attempts to determine if the user is authorized to access the
resource. Many of these checks require
mod_auth_ldap to do a compare operation on the
LDAP server. This is why this phase is often referred to as the
mod_auth_ldap accepts the
directives to determine if the credentials are acceptable:
- Grant access if there is a
- Grant access if there is a
Require userdirective, and the username in the directive matches the username passed by the client.
- Grant access if there is a
Require dndirective, and the DN in the directive matches the DN fetched from the LDAP directory.
- Grant access if there is a
Require groupdirective, 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-attributedirective, and the attribute fetched from the LDAP directory matches the given value.
- otherwise, deny or decline access
mod_auth_ldap uses the following directives during the
||The attribute specified in the
URL is used in compare operations for the
||Determines the behavior of the
||Determines the attribute to
use for comparisons in the
||Specifies whether to use the
user DN or the username when doing comparisons for the
directives are used during the authorization phase to ensure that
a user is allowed to access a resource.
If this directive exists,
access to any user that has successfully authenticated during the
Require user directive specifies what
usernames can access the resource. Once
mod_auth_ldap has retrieved a unique DN from the
directory, it does an LDAP compare operation using the username
specified in the
Require 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
directives, with one user per line. For example, with a
used for searches), the following Require directives could be used
to restrict access:
Require user "Barbara Jenson"
Require user "Fred User"
Require user "Joe Manager"
Because of the way that
mod_auth_ldap handles this
directive, Barbara Jenson could sign on as Barbara
Jenson, Babs Jenson or any other
she has in her LDAP entry. Only the single
user line is needed to support all values of the attribute
in the user's entry.
uid attribute was used instead of the
cn attribute in the URL above, the above three lines
could be condensed to
Require user bjenson fuser jmanager
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:
dn: cn=Administrators, o=Airius
uniqueMember: cn=Barbara Jenson, o=Airius
uniqueMember: cn=Fred User, o=Airius
The following directive would grant access to both Fred and Barbara:
Require group cn=Administrators, o=Airius
Require 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 dn, then
authorization is granted. Note: do not surround the distinguished
name with quotes.
The following directive would grant access to a specific DN:
Require dn cn=Barbara Jenson, o=Airius
Behavior of this directive is modified by 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
Require ldap-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 a
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"
Require ldap-attribute city="San Jose" status=active
Grant access to anyone who exists in the LDAP directory,
using their UID for searches.
AuthLDAPURL "ldap://ldap1.airius.com:389/ou=People, o=Airius?uid?sub?(objectClass=*)"
The next example is the same as above; but with the fields
that have useful defaults omitted. Also, note the use of a
redundant LDAP server.
AuthLDAPURL "ldap://ldap1.airius.com ldap2.airius.com/ou=People, o=Airius"
The next example is similar to the previous one, but is
uses the common name instead of the UID. Note that this
could be problematical if multiple people in the directory
share the same
cn, because a search on
cnmust return exactly one entry. That's why this approach is not recommended: it's a better idea to choose an attribute that is guaranteed unique in your directory, such as
AuthLDAPURL "ldap://ldap.airius.com/ou=People, o=Airius?cn"
Grant access to anybody in the Administrators group. The
users must authenticate using their UID.
Require group cn=Administrators, o=Airius
The next example assumes that everyone at Airius who
carries an alphanumeric pager will have an LDAP attribute
qpagePagerID. The example will grant access only to people (authenticated via their UID) who have alphanumeric pagers:
The next example demonstrates the power of using filters to accomplish complicated administrative requirements. Without filters, it would have been necessary to create a new LDAP group and ensure that the group's members remain synchronized with the pager users. This becomes trivial with filters. The goal is to grant access to anyone who has a filter, plus grant access to Joe Manager, who doesn't have a pager, but does need to access the same resource:
This last may look confusing at first, so it helps to evaluate what the search filter will look like based on who connects, as shown below. The text in blue is the part that is filled in using the attribute specified in the URL. The text in red is the part that is filled in using the filter specified in the URL. The text in green is filled in using the information that is retrieved from the HTTP client. If Fred User connects as
fuser, the filter would look like
The above search will only succeed if fuser has a pager. When Joe Manager connects as jmanager, the filter looks like
The above search will succeed whether jmanager has a pager or not.
To specify a secure LDAP server, use ldaps:// in the
directive, instead of ldap://.
Normally, FrontPage uses FrontPage-web-specific user/group
files (i.e., the
mod_auth module) to handle all
authentication. Unfortunately, it is not possible to just
change to LDAP authentication by adding the proper directives,
because it will break the Permissions forms in
the FrontPage client, which attempt to modify the standard
text-based authorization files.
Once a FrontPage web has been created, adding LDAP
authentication to it is a matter of adding the following
directives to every
that gets created in the web
AuthLDAPURL "the url" AuthLDAPAuthoritative off AuthLDAPFrontPageHack on
AuthLDAPAuthoritative must be
off to allow
mod_auth_ldap to decline group
authentication so that Apache will fall back to file
authentication for checking group membership. This allows the
FrontPage-managed group file to be used.
FrontPage restricts access to a web by adding the
valid-user directive to the
AuthLDAPFrontPageHack is not
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. The purpose of the hack is to force Apache to consult the
local user file (which is managed by FrontPage) - instead of LDAP
- when handling the
Require valid-user directive.
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_authuser 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_authin order to use FrontPage support. This is because Apache will still use the
mod_authgroup file for determine the extent of a user's access to the FrontPage web.
- The directives must be put in the
.htaccessfiles. Attempting to put them inside
<Directory>directives won't work. This is because
mod_auth_ldaphas to be able to grab the
AuthUserFiledirective that is found in FrontPage
.htaccessfiles so that it knows where to look for the valid user list. If the
mod_auth_ldapdirectives aren't in the same
.htaccessfile as the FrontPage directives, then the hack won't work, because
mod_auth_ldapwill never get a chance to process the
.htaccessfile, and won't be able to find the FrontPage-managed user file.
|Description:||Prevent other authentication modules from authenticating the user if this one fails|
off if this module should let other
authentication modules attempt to authenticate the user, should
authentication with this module fail. Control is only passed on
to lower modules if there is no DN or rule that matches the
supplied user name (as passed by the client).
|Description:||Optional DN to use in binding to the LDAP server|
An optional DN used to bind to the server when searching for
entries. If not provided,
mod_auth_ldap will use
an anonymous bind.
|Description:||Password used in conjuction with the bind DN|
A bind password to use in conjunction with the bind DN. Note
that the bind password is probably sensitive data, and should be
properly protected. You should only use the
AuthLDAPBindPassword if you
absolutely need them to search the directory.
|Description:||Language to charset conversion configuration file|
AuthLDAPCharsetConfig directive sets the location
of the language to charset conversion configuration file. File-path is relative
ServerRoot. This file specifies
the list of language extensions to character sets.
Most administrators use the provided
file, which associates common language extensions to character sets.
The file contains lines in the following format:
Language-Extension charset [Language-String] ...
The case of the extension does not matter. Blank lines, and lines
beginning with a hash character (
#) are ignored.
|Description:||Use the LDAP server to compare the DNs|
mod_auth_ldap will use the LDAP
server to compare the DNs. This is the only foolproof way to
mod_auth_ldap will search the
directory for the DN specified with the
Require dn directive, then,
retrieve the DN and compare it with the DN retrieved from the user
entry. If this directive is not set,
mod_auth_ldap simply does a string comparison. It
is possible to get false negatives with this approach, but it is
much faster. Note the
mod_ldap cache can speed up
DN comparison in most situations.
|Description:||When will the module de-reference aliases|
This directive specifies when
de-reference aliases during LDAP operations. The default is
|Description:||Turn on or off LDAP authentication|
|Description:||Allow LDAP authentication to work with MS FrontPage|
|Description:||LDAP attributes used to check for group membership|
This directive specifies which LDAP attributes are used to
check for group membership. Multiple attributes can be used by
specifying this directive multiple times. If not specified,
mod_auth_ldap uses the
|Description:||Use the DN of the client username when checking for group membership|
on, this directive says to use the
distinguished name of the client username when checking for group
membership. Otherwise, the username will be used. For example,
assume that the client sent the username
which corresponds to the LDAP DN
o=Airius. If this directive is set,
mod_auth_ldap will check if the group has
cn=Babs Jenson, o=Airius as a member. If this
directive is not set, then
check if the group has
bjenson as a member.
|Description:||Use the DN of the client username to set the REMOTE_USER environment variable|
If this directive is set to on, the value of the
REMOTE_USER environment variable will be set to the full
distinguished name of the authenticated user, rather than just
the username that was passed by the client. It is turned off by
|Description:||URL specifying the LDAP search parameters|
An RFC 2255 URL which specifies the LDAP search parameters to use. The syntax of the URL is
- For regular ldap, use the
ldap. For secure LDAP, use
ldapsinstead. Secure LDAP is only available if Apache was linked to an LDAP library with SSL support.
The name/port of the ldap server (defaults to
ldaps). To specify multiple, redundant LDAP servers, just list all servers, separated by spaces.
mod_auth_ldapwill try connecting to each server in turn, until it makes a successful connection.
Once a connection has been made to a server, that connection remains active for the life of the
httpdprocess, or until the LDAP server goes down.
If the LDAP server goes down and breaks an existing connection,
mod_auth_ldapwill attempt to re-connect, starting with the primary server, and trying each redundant server in turn. Note that this is different than a true round-robin search.
- The DN of the branch of the directory where all searches should start from. At the very least, this must be the top of your directory tree, but could also specify a subtree in the directory.
- The attribute to search for.
Although RFC 2255 allows a comma-separated list of
attributes, only the first attribute will be used, no
matter how many are provided. If no attributes are
provided, the default is to use
uid. It's a good idea to choose an attribute that will be unique across all entries in the subtree you will be using.
- The scope of the search. Can be either
sub. Note that a scope of
baseis also supported by RFC 2255, but is not supported by this module. If the scope is not provided, or if
basescope is specified, the default is to use a scope of
- A valid LDAP search filter. If
not provided, defaults to
(objectClass=*), which will search for all objects in the tree. Filters are limited to approximately 8000 characters (the definition of
MAX_STRING_LENin the Apache source code). This should be than sufficient for any application.
When doing searches, the attribute, filter and username passed
by the HTTP client are combined to create a search filter that
For example, consider an URL of
a client attempts to connect using a username of
Jenson, the resulting search filter will be
See above for examples of