Apache HTTP Server Version 2.2
Apache Module mod_authnz_ldap
|Description:||Allows an LDAP directory to be used to store the database for HTTP Basic authentication.|
|Compatibility:||Available in version 2.1 and later|
This module provides authentication front-ends such as
mod_auth_basic to authenticate users through
an ldap directory.
mod_authnz_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.
- 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).
- The Require Directives
- Using TLS
- Using SSL
- Exposing Login Information
Using Microsoft FrontPage with
There are two phases in granting access to a user. The first
phase is authentication, in which the
authentication provider verifies that the user's credentials are valid.
This is 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
mod_authnz_ldap registers both an authn_ldap authentication
provider and an authz_ldap authorization handler. The authn_ldap
authentication provider can be enabled through the
ldap value. The authz_ldap handler extends the
Require directive's authorization types
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_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.
- 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_authnz_ldap to do a compare operation on the
LDAP server. This is why this phase is often referred to as the
mod_authnz_ldap accepts the
directives to determine if the credentials are acceptable:
- Grant access if there is a
Require ldap-userdirective, and the username in the directive matches the username passed by the client.
- Grant access if there is a
Require ldap-dndirective, and the DN in the directive matches the DN fetched from the LDAP directory.
- Grant access if there is a
Require ldap-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.
- Grant access if there is a
Require ldap-filterdirective, and the search filter successfully finds a single user object that matches the dn of the authenticated user.
- otherwise, deny or decline access
Require values may also
be used which may require loading additional authorization modules.
Note that if you use a
value from another authorization module, you will need to ensure that
is set to
off to allow the authorization phase to fall
back to the module providing the alternate
Require value. When no
are used, authorization is allowed to fall back to other modules
was set to
- Grant access to all successfully authenticated users if
there is a
Require valid-userdirective. (requires
- Grant access if there is a
Require groupdirective, and
mod_authz_groupfilehas been loaded with the
mod_authnz_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. mod_authnz_ldap extends the
authorization types with
ldap-filter. Other authorization types may also be
used but may require that additional authorization modules be loaded.
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
directives, with one user per line. For example, with a
used for searches), the following Require directives could be used
to restrict access:
Require ldap-user "Barbara Jenson"
Require ldap-user "Fred User"
Require ldap-user "Joe Manager"
Because of the way that
mod_authnz_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
ldap-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 ldap-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 ldap-group cn=Administrators, o=Airius
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:
Require ldap-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 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"
Require ldap-attribute city="San Jose" status=active
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
Require ldap-filter &(cell=*)(department=marketing)
The difference between the
Require ldap-filter directive and the
Require ldap-attribute directive is that
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
ldap-filter especially within a large directory.
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 it
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 ldap-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 pager, 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. 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.
An optional second parameter can be added to the
AuthLDAPURL to override
the default connection type set by
This will allow the connection established by an ldap:// Url
to be upgraded to a secure connection on the same port.
To specify a secure LDAP server, use ldaps:// in the
directive, instead of ldap://.
When this module performs authentication, LDAP attributes specified
directive are placed in environment variables with the prefix "AUTHENTICATE_".
If the attribute field contains the username, common name and telephone number of a user, a CGI program will have access to this information without the need to make a second independent LDAP query to gather this additional information.
This has the potential to dramatically simplify the coding and configuration required in some web applications.
Normally, FrontPage uses FrontPage-web-specific user/group
files (i.e., the
mod_authz_groupfile modules) 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" AuthGroupFile mygroupfile Require group mygroupfile
FrontPage restricts access to a web by adding the
valid-user directive to 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_fileuser 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_authz_groupfilein order to use FrontPage support. This is because Apache will still use the
mod_authz_groupfilegroup 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_authnz_ldaphas to be able to grab the
AuthGroupFiledirective that is found in FrontPage
.htaccessfiles so that it knows where to look for the valid user list. If the
mod_authnz_ldapdirectives aren't in the same
.htaccessfile as the FrontPage directives, then the hack won't work, because
mod_authnz_ldapwill never get a chance to process the
.htaccessfile, and won't be able to find the FrontPage-managed user file.
|Description:||Determines if other authentication providers are used when a user can be mapped to a DN but the server cannot successfully bind with the user's credentials.|
|Compatibility:||Available in versions later than 2.2.14|
By default, subsequent authentication providers are only queried if a
user cannot be mapped to a DN, but not if the user can be mapped to a DN and their
password cannot be verified with an LDAP bind.
is set to off, other configured authentication modules will have
a chance to validate the user if the LDAP bind (with the current user's credentials)
fails for any reason.
This allows users present in both LDAP and
AuthUserFile to authenticate
when the LDAP server is available but the user's account is locked or password
is otherwise unusable.
|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_authnz_ldap will use
an anonymous bind.
|Description:||Password used in conjuction with the bind DN|
|Compatibility:||exec: was added in 2.2.25.|
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.
If the value begins with exec: the resulting command will be executed and the first line returned to standard output by the program will be used as the password.
#Password used as-is AuthLDAPBindPassword secret #Run /path/to/program to get my password AuthLDAPBindPassword exec:/path/to/program #Run /path/to/otherProgram and provide arguments AuthLDAPBindPassword "exec:/path/to/otherProgram argument1"
|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_authnz_ldap will use the LDAP
server to compare the DNs. This is the only foolproof way to
mod_authnz_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_authnz_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:||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_authnz_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_authnz_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 value of the attribute returned during the user query to set the REMOTE_USER environment variable|
If this directive is set, the value of the
REMOTE_USER environment variable will be set to the
value of the attribute specified. Make sure that this attribute is
included in the list of attributes in the AuthLDAPUrl definition,
otherwise this directive will have no effect. This directive, if
present, takes precedence over AuthLDAPRemoteUserIsDN. This
directive is useful should you want people to log into a website
using an email address, but a backend application expects the
username as a userid.
|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_authnz_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_authnz_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 more 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
An optional parameter can be added to allow the LDAP Url to override the connection type. This parameter can be one of the following:
- Establish an unsecure connection on the default LDAP port. This
is the same as
ldap://on port 389.
- Establish a secure connection on the default secure LDAP port.
This is the same as
- TLS | STARTTLS
- Establish an upgraded secure connection on the default LDAP port. This connection will be initiated on port 389 by default and then upgraded to a secure connection on the same port.
See above for examples of
is enabled in a particular context, but some other module has performed
authentication for the request, the server will try to map the username to a DN
during authorization regardless of whether or not LDAP-specific requirements
are present. To ignore the failures to map a username to a DN during
AuthzLDAPAuthoritative to "off".
|Description:||Prevent other authentication modules from authenticating the user if this one fails|
off if this module should let other
authorization modules attempt to authorize the user, should
authorization 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).