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V4/Allow AD users to manage FreeIPA

Name: V4/Allow AD users to manage FreeIPA
Ticket: #TODO
Target version: 4.4.x
Author: Ab
Incomplete.png Pending review
Last updated: 2016-06-14 by Ab

Overview

Allow Active Directory users to use FreeIPA command line interface (CLI) to manage FreeIPA resources

Use Cases

A forest trust is established between FreeIPA and Active Directory, most of the users and groups are defined in Active Directory. Allow Active Directory users to gain access to IPA CLI and manage resources defined in FreeIPA with the help of IPA CLI.

Design

FreeIPA management framework authenticates users with Kerberos or user name/password pair. For the latter case it obtains a ticket using the user name and password and further uses Kerberos authentication against other FreeIPA resources. Primary resource accessed with Kerberos credentials by FreeIPA management framework is LDAP server. Kerberos credentials aren't forwarded to FreeIPA management framework; instead, it uses Kerberos S4U2Proxy mechanism to request Kerberos ticket to LDAP server on behalf of the user.

  • FreeIPA management framework uses Kerberos credentials to authenticate to LDAP server.
  • FreeIPA LDAP server uses SASL mapping configuration to translate successfully authenticated Kerberos principal to an object in LDAP
  • Object in LDAP that corresponds to the Kerberos principal as result of SASL mapping process is then subjected to LDAP ACIs when identifying actual access rights to specific attributes of LDAP objects accessed.

Thus, in order to allow Active Directory users to authenticate to FreeIPA framework and to FreeIPA LDAP server, one needs to make sure Active Directory users are mapped to *some* LDAP objects that can be used to define access in LDAP ACIs.

FreeIPA provides a mechanism called *ID Overrides* to associate certain POSIX attributes with Active Directory users. ID override for the user is a normal LDAP object which can be used to map a Kerberos identity of an Active Directory user to itself. This LDAP object then can be added as a member to other FreeIPA groups that define permissions and roles in the FreeIPA framework.

Implementation

FreeIPA LDAP server supports multiple SASL maps. Each map is supposed to produce a unique match between SASL identity and an LDAP object. If there is a match, a matched LDAP object's DN is used as a resulted DN of LDAP BIND operation.

FreeIPA ID Views support multiple views for overriding Active Directory users and groups. Since a unique match is required, a 'Default Trust View' ID view is used to provide a mapping. This is implemented with a SASL mapping introduced in this git commit. SASL mapping is not replicated because it is part of cn=config tree in LDAP, thus every single FreeIPA master needs to be updated in order to enable access by Active Directory users over LDAP.

ID override for an Active Directory user in 'Default Trust View' can be added to any LDAP group to allow it to be a member of that group. However, FreeIPA includes a special plugin, called "Member Of plugin" that propagates information about membership back to the LDAP object which became a member of a group in LDAP. In order to do so, object classes associated with the LDAP object must allow 'memberof' attribute. If 'memberof' attribute is not allowed, the operation to add ID override as a member of any LDAP group in FreeIPA LDAP server will fail. Thus, ID override entry needs to allow 'memberof' attribute.

An easiest way to allow 'memberof' attribute is to allow it as part of ipaUserOverride class:

objectClasses: (2.16.840.1.113730.3.8.12.31 NAME 'ipaUserOverride' DESC 'Override for User Attributes' SUP ipaOverrideAnchor STRUCTURAL MAY ( uid $ uidNumber $ gidNumber $ homeDirectory $ loginShell $ gecos $ ipaOriginalUid $ userCertificate $ memberOf) X-ORIGIN 'IPA v4' )

A change like this requires schema update.

Finally, ipa group-add-member command should be extended to allow specifying Active Directory users in --users option using fully qualified user name syntax. Following logic should be used as soon as '@' character is detected in --users option value:

  • try to resolve the user to SID
  • if succeeded, see if ID override for this user exists in Default trust view
  • if no ID override exist, add it to Default trust view (no attributes to override is just fine)
  • if succeeded, add DN of the override to the group membership list

Feature Management

UI

Currently the feature is aimed for use in CLI in the first stage.

CLI

Overview of the CLI commands. The only change is to modify existing group management commands to allow specifying trusted domain users through fully qualified names:

Command Options Comment
group-add-member --users=administrator@ad.domain Add trusted domain user to a group. If ID override for this user is missing, add it to 'Default Trust View'
group-remove-member --users=administrator@ad.domain Remove trusted domain user to from a group.
group-show Show members that are trusted domain users

Configuration

Upgrade

Any impact on upgrades? Remove this section if not applicable.

How to Use

Easy to follow instructions how to use the new feature according to the use cases described above. FreeIPA user needs to be able to follow the steps and demonstrate the new features.

The chapter may be divided in sub-sections per Use Case.

Test Plan

Test scenarios that will be transformed to test cases for FreeIPA Continuous Integration during implementation or review phase. This can be also link to source in cgit with the test, if appropriate.