mod_authnz_ldap
Allows an LDAP directory to be used to store the database for HTTP Basic authentication.
Extension
mod_authnz_ldap.c
authnz_ldap_module
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).

When using mod_auth_basic, this module is invoked via the AuthBasicProvider directive with the `ldap` value.

mod_ldap
mod_auth_basic
mod_authz_user
mod_authz_groupfile

# Contents

- Operation

  - The Authentication Phase
  - The Authorization Phase
- The require Directives

  - require valid-user
  - require ldap-user
  - require ldap-group
  - require ldap-dn
- Examples
- Using TLS
- Using SSL
- Using Microsoft FrontPage with mod_authnz_ldap

  - How It Works
  - Caveats

# Operation

There are two phases in granting access to a user. The first phase is authentication, in which the mod_authnz_ldap 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 mod_authnz_ldap determines if the authenticated user is allowed access to the resource in question. This is also known as the compare phase.

mod_authnz_ldap registers both an authn_ldap authentication provider and an anthz_ldap authorization handler. The authn_ldap authentication provider can be enabled through the AuthBasicProvider directive using the `ldap` value. The authz_ldap handler extends the Require directive's authorization types by adding `ldap-user`, `ldap-dn` and `ldap-group` values.

## The Authentication Phase

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

AuthLDAPURL | Specifies the LDAP server, the base DN, the attribute to use in the search, as well as the extra search filter to use.
AuthLDAPBindDN | An optional DN to bind with during the search phase.
AuthLDAPBindPassword | An optional password to bind with during the search phase.

## The Authorization 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.
- 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:

AuthLDAPURL | The attribute specified in the URL is used in compare operations for the `require user` operation.
AuthLDAPCompareDNOnServer | Determines the behavior of the `require dn` directive.
AuthLDAPGroupAttribute | Determines the attribute to use for comparisons in the `require group` directive.
AuthLDAPGroupAttributeIsDN | Specifies whether to use the user DN or the username when doing comparisons for the `require group` directive.

# The require Directives

Apache's Require 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-user`, `ldap-dn` and `ldap-group`. Other authorization types may also be used but may require that additional authorization modules be loaded.

## require valid-user

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 AuthLDAPAuthoritative directive be set to off.

## require ldap-user

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:

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 `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

require ldap-user bjenson fuser jmanager

## require ldap-group

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
objectClass: groupOfUniqueNames
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

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

## require ldap-dn

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:

require ldap-dn cn=Barbara Jenson, o=Airius

Behavior of this directive is modified by the AuthLDAPCompareDNOnServer directive.

# Examples

- 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=*)
  require valid-user
- 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
  require valid-user
- 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 `cn` must 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 `uid`. AuthLDAPURL ldap://ldap.airius.com/ou=People, o=Airius?cn
  require valid-user
- Grant access to anybody in the Administrators group. The users must authenticate using their UID. AuthLDAPURL ldap://ldap.airius.com/o=Airius?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 of `qpagePagerID`. The example will grant access only to people (authenticated via their UID) who have alphanumeric pagers: AuthLDAPURL ldap://ldap.airius.com/o=Airius?uid??(qpagePagerID=*)
  require valid-user

- 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:

  AuthLDAPURL ldap://ldap.airius.com/o=Airius?uid??(|(qpagePagerID=*)(uid=jmanager))
  require valid-user

  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

  (&(|(qpagePagerID=*)(uid=jmanager))(uid=fuser))

  The above search will only succeed if fuser has a pager. When Joe Manager connects as jmanager, the filter looks like

  (&(|(qpagePagerID=*)(uid=jmanager))(uid=jmanager))

  The above search will succeed whether jmanager has a pager or not.

# Using TLS

To use TLS, see the mod_ldap directives LDAPTrustedCA and LDAPTrustedCAType.

# Using SSL

To use SSL, see the mod_ldap directives LDAPTrustedCA and LDAPTrustedCAType.

To specify a secure LDAP server, use ldaps:// in the AuthLDAPURL directive, instead of ldap://.

# Using Microsoft FrontPage with mod_authnz_ldap

Normally, FrontPage uses FrontPage-web-specific user/group files (i.e., the mod_authn_file and 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 `.htaccess` file that gets created in the web

    AuthLDAPURL            "the url"
    AuthLDAPAuthoritative  off
    AuthGroupFile mygroupfile
    require group mygroupfile

AuthLDAPAuthoritative must be off to allow mod_authnz_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.

## How It Works

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.

## Caveats

- 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.

AuthLDAPAuthoritative
Prevent other authentication modules from authenticating the user if this one fails
AuthLDAPAuthoritative on|off
AuthLDAPAuthoritative on
directory
.htaccess
AuthConfig

Set to `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).

AuthLDAPBindDN
Optional DN to use in binding to the LDAP server
AuthLDAPBindDN distinguished-name
directory
.htaccess
AuthConfig

An optional DN used to bind to the server when searching for entries. If not provided, mod_authnz_ldap will use an anonymous bind.

AuthLDAPBindPassword
Password used in conjuction with the bind DN
AuthLDAPBindPassword password
directory
.htaccess
AuthConfig

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 AuthLDAPBindDN and AuthLDAPBindPassword if you absolutely need them to search the directory.

AuthLDAPCharsetConfig
Language to charset conversion configuration file
AuthLDAPCharsetConfig file-path
server config

The AuthLDAPCharsetConfig directive sets the location of the language to charset conversion configuration file. File-path is relative to the ServerRoot. This file specifies the list of language extensions to character sets. Most administrators use the provided `charset.conv` 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.

AuthLDAPCompareDNOnServer
Use the LDAP server to compare the DNs
AuthLDAPCompareDNOnServer on|off
AuthLDAPCompareDNOnServer on
directory
.htaccess
AuthConfig

When set, mod_authnz_ldap will use the LDAP server to compare the DNs. This is the only foolproof way to compare DNs. 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.

AuthLDAPDereferenceAliases
When will the module de-reference aliases
AuthLDAPDereferenceAliases never|searching|finding|always
AuthLDAPDereferenceAliases Always
directory
.htaccess
AuthConfig

This directive specifies when mod_authnz_ldap will de-reference aliases during LDAP operations. The default is `always`.

AuthLDAPGroupAttribute
LDAP attributes used to check for group membership
AuthLDAPGroupAttribute attribute
directory
.htaccess
AuthConfig

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, then mod_authnz_ldap uses the `member` and `uniquemember` attributes.

AuthLDAPGroupAttributeIsDN
Use the DN of the client username when checking for group membership
AuthLDAPGroupAttributeIsDN on|off
AuthLDAPGroupAttributeIsDN on
directory
.htaccess
AuthConfig

When set `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 `bjenson`, which corresponds to the LDAP DN `cn=Babs Jenson, 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 mod_authnz_ldap will check if the group has `bjenson` as a member.

AuthLDAPRemoteUserIsDN
Use the DN of the client username to set the REMOTE_USER environment variable
AuthLDAPRemoteUserIsDN on|off
AuthLDAPRemoteUserIsDN off
directory
.htaccess
AuthConfig

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 default.

AuthLDAPUrl
URL specifying the LDAP search parameters
AuthLDAPUrl url
directory
.htaccess
AuthConfig

An RFC 2255 URL which specifies the LDAP search parameters to use. The syntax of the URL is

ldap://host:port/basedn?attribute?scope?filter

ldap
  For regular ldap, use the string `ldap`. For secure LDAP, use `ldaps` instead. Secure LDAP is only available if Apache was linked to an LDAP library with SSL support.
host:port

  The name/port of the ldap server (defaults to `localhost:389` for `ldap`, and `localhost:636` for `ldaps`). To specify multiple, redundant LDAP servers, just list all servers, separated by spaces. mod_authnz_ldap will 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 `httpd` process, or until the LDAP server goes down.

  If the LDAP server goes down and breaks an existing connection, mod_authnz_ldap will 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.

basedn
  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.
attribute
  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.
scope
  The scope of the search. Can be either `one` or `sub`. Note that a scope of `base` is also supported by RFC 2255, but is not supported by this module. If the scope is not provided, or if `base` scope is specified, the default is to use a scope of `sub`.
filter
  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_LEN` in 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 looks like `(&(filter)(attribute=username))`.

For example, consider an URL of `ldap://ldap.airius.com/o=Airius?cn?sub?(posixid=*)`. When a client attempts to connect using a username of `Babs Jenson`, the resulting search filter will be `(&(posixid=*)(cn=Babs Jenson))`.

See above for examples of AuthLDAPURL URLs.