V4/Support of UPN for trusted domains
User principal name (UPN) in Active Directory is the primary form of addressing users. UPN has structure of 'user name@suffix' where both user name and suffix parts may vary. By default the suffix is the same as the Active Directory domain name but AD administrators may create additional name suffixes and associate them with specific users. These additional UPNs for users may then be used for Kerberos authentication against Active Directory domains.
Alternative UPNs are often used when several companies with Active Directory deployments merge and want to provide unified logon namespace.
The purpose of this feature is to allow using alternative UPNs associated with the Active Directory users when accessing resources in FreeIPA domain.
As an Active Directory user, I want to login using my user@EXAMPLE user principal name even if my Active Directory domain is named REGION.EXAMPLE.COM.
Support for UPNs is split to three different components:
- SSSD already supports logon with UPN by asking a KDC to accept enterprise logon names. By default, the use of enterprise principals is disabled, therefore,
krb5_use_enterprise_principal = Trueneeds to be added to sssd.conf to enable it.
- IPA KDC does understand multiple domains associated with the trusted AD forest. However, since no information about name suffixes associated with the forest is available, it cannot take them into account when processing enteprise logon names to issue referrals to the correct realm. Support needs to be added to allow IPA KDC to look up name suffixes associated with a trusted forest.
- IPA framework
- Changes needed on IPA framework side to fetch from Active Directory a list of name suffixes and store them in the trusted domain objects.
For retrieving name suffixes, IPA framework needs to move to use NETLOGON netr_DsRGetForestTrustInformation function instead of netr_DsrEnumerateDomainTrusts. This allows to retrieve both domains and top level names associated with the forest.
As top level names (TLNs) have only a single string as a name suffix, they cannot be stored as trusted domains (they lack SID and NetBIOS name). Thus, either IPA KDB driver needs to be extended to understand trusted domains without SID and NetBIOS name, or TLNs need to be stored as a property of tree root domains of the forest.
TLNs are added as a property of tree root domains of the forest, appropriate panel needs to be extended to display them.
When TLNs are added as a property of tree root domains of the forest, appropriate attribute need to be handled by trust-show command.
No configuration options.
An attribute 'ipaNTAdditionalSuffixes' is added to 'ipaNTTrustedDomain' object class. Replicas which are not upgraded to the FreeIPA version which contains the attribute and changed object class definition, will receive schema changes as part of replication. The IPA framework running on non-upgraded replica will not be able to fill-in the attribute values and will not be able to show it until the packages for the FreeIPA framework are upgraded.
How to Test
In order to test UPN-based logons, create additional name suffixes in Active Directory and establish trust to it. After trust is established, the name suffixes should be usable when trying to kinit as enterprise principal.
See https://technet.microsoft.com/en-us/library/cc739093%28v=ws.10%29.aspx for details of AD naming and how to add UPNs.