Contents

• Operation
  • The Authentication Phase
  • The Authorization Phase
• The require Directives
  • require valid-user
  • require ldap-user
  • require ldap-group
  • require ldap-dn
  • require ldap-attribute
  • require ldap-filter
• Examples
• Using TLS
• Using SSL
• Using Microsoft FrontPage withmod_authnz_ldap
  • How It Works
  • Caveats

Operation

There are two phases in granting access to a user. The first phase is authentication, in which themod_authnz_ldapauthentication provider verifies that the user's credentials are valid. This is also called thesearch/bindphase. The second phase is authorization, in whichmod_authnz_ldapdetermines if the authenticated user is allowed access to the resource in question. This is also known as thecomparephase.

mod_authnz_ldapregisters both an authn_ldap authentication provider and an authz_ldap authorization handler. The authn_ldap authentication provider can be enabled through theAuthBasicProviderdirective using theldapvalue. The authz_ldap handler extends theRequiredirective's authorization types by addingldap-user,ldap-dn和ldap-groupvalues.

The Authentication Phase

During the authentication phase,mod_authnz_ldapsearches for an entry in the directory that matches the username that the HTTP client passes. If a single unique match is found, thenmod_authnz_ldapattempts 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 theAuthLDAPURLdirective 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

The Authorization Phase

During the authorization phase,mod_authnz_ldapattempts to determine if the user is authorized to access the resource. Many of these checks requiremod_authnz_ldapto do a compare operation on the LDAP server. This is why this phase is often referred to as the compare phase.mod_authnz_ldapaccepts the followingRequiredirectives to determine if the credentials are acceptable:

• Grant access if there is arequire ldap-userdirective, and the username in the directive matches the username passed by the client.
• Grant access if there is arequire ldap-dndirective, and the DN in the directive matches the DN fetched from the LDAP directory.
• Grant access if there is arequire 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 arequire ldap-attributedirective, and the attribute fetched from the LDAP directory matches the given value.
• Grant access if there is arequire 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

OtherRequirevalues may also be used which may require loading additional authorization modules.

• Grant access if there is arequire valid-userdirective. (requiresmod_authz_user)
• Grant access if there is arequire groupdirective, andmod_authz_groupfilehas been loaded with theAuthGroupFiledirective set.
• others...

mod_authnz_ldapuses the following directives during the compare phase:

The require Directives

Apache'sRequiredirectives are used during the authorization phase to ensure that a user is allowed to access a resource. mod_authnz_ldap extends the authorization types withldap-user,ldap-dn,ldap-group,ldap-attribute和ldap-filter. 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_ldapgrants access to any user that has successfully authenticated during the search/bind phase. Requires thatmod_authz_userbe loaded and that theAuthzLDAPAuthoritativedirective be set to off.

require ldap-user

require ldap-userdirective specifies what usernames can access the resource. Oncemod_authnz_ldaphas retrieved a unique DN from the directory, it does an LDAP compare operation using the username specified in therequire ldap-userto 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 multiplerequire ldap-userdirectives, with one user per line. For example, with aAuthLDAPURLofldap://ldap/o=Airius?cn(i.e.,cnis used for searches), the following require directives could be used to restrict access:

Because of the way thatmod_authnz_ldaphandles this directive, Barbara Jenson could sign on asBarbara Jenson,Babs Jensonor any othercnthat she has in her LDAP entry. Only the singlerequire ldap-userline is needed to support all values of the attribute in the user's entry.

If theuidattribute was used instead of thecnattribute in the URL above, the above three lines could be condensed to

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:

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

Behavior of this directive is modified by theAuthLDAPGroupAttribute和AuthLDAPGroupAttributeIsDNdirectives.

require ldap-dn

require ldap-dndirective 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 therequire 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 theAuthLDAPCompareDNOnServerdirective.

require ldap-attribute

require ldap-attributedirective 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 multiplerequire ldap-attributedirectives. 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-filter

require ldap-filterdirective 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 therequire ldap-filterdirective and therequire ldap-attributedirective is thatldap-filterperforms 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 byldap-attributewill be faster than the search operation used byldap-filterespecially within a large directory.

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 it uses the common name instead of the UID. Note that this could be problematical if multiple people in the directory share the samecn, because a search oncnmustreturn 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 asuid.

  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 ofqpagePagerID. 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 pager, 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. If Fred User connects asfuser, the filter would look like

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

  The above search will only succeed iffuserhas a pager. When Joe Manager connects asjmanager, the filter looks like

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

  The above search will succeed whetherjmanagerhas a pager or not.

Using TLS

To use TLS, see themod_ldapdirectivesLDAPTrustedClientCert,LDAPTrustedGlobalCert和LDAPTrustedMode.

An optional second parameter can be added to theAuthLDAPURLto override the default connection type set byLDAPTrustedMode. This will allow the connection established by anldap://Url to be upgraded to a secure connection on the same port.

Using SSL

To use SSL, see themod_ldapdirectivesLDAPTrustedClientCert,LDAPTrustedGlobalCert和LDAPTrustedMode.

To specify a secure LDAP server, useldaps://in theAuthLDAPURLdirective, instead ofldap://.

Using Microsoft FrontPage with mod_authnz_ldap

Normally, FrontPage uses FrontPage-web-specific user/group files (i.e., themod_authn_file和mod_authz_groupfilemodules) to handle all authentication. Unfortunately, it is not possible to just change to LDAP authentication by adding the proper directives, because it will break thePermissionsforms 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 toevery.htaccessfile that gets created in the web

AuthLDAPURL "the url" AuthzLDAPAuthoritative off AuthGroupFilemygroupfilerequire groupmygroupfile

AuthzLDAPAuthoritativemust be off to allowmod_authnz_ldapto 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 therequire valid-userdirective to the.htaccessfiles. Therequire valid-userdirective will succeed for any user who is validas 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 amod_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 withmod_auth_basic,mod_authn_file和mod_authz_groupfilein order to use FrontPage support. This is because Apache will still use themod_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或directives won't work. This is becausemod_authnz_ldaphas to be able to grab theAuthGroupFiledirective that is found in FrontPage.htaccessfiles so that it knows where to look for the valid user list. If themod_authnz_ldapdirectives aren't in the same.htaccessfile as the FrontPage directives, then the hack won't work, becausemod_authnz_ldapwill never get a chance to process the.htaccessfile, and won't be able to find the FrontPage-managed user file.