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V4/Certificate Identity Mapping

Name: V4/Certificate Identity Mapping
Ticket: #6542
Target version: 4.5.0
Author: frenaud
Incomplete.png Pending review
Last updated: 2017-06-6 by Frenaud

Overview

FreeIPA already supports Smart Card authentication: the user provides a Smart Card containing a certificate and the user lookup is performed with a binary match of the whole certificate (see User Certificates).

The goal is to extend this feature to support the following cases:

  • the Smart Card contains multiple certificates. The administrator must be able to define Matching rules that will check which certificates are valid for authentication.
  • the Smart Card contains multiple certificates that are valid for authentication. The user must be able to select the certificate he wants to use for login.
  • the Certificate presented by the user is mapped to multiple accounts. The user must be able to disambiguate by providing a username.
  • the mapping between a Certificate and a user account can be done either through binary match of the whole certificate or a match on custom certificate attributes (such as Subject + Issuer).


The feature is tightly linked to SSSD features:

Use Cases

  • As a user with multiple accounts linked to my Smart Card certificate in FreeIPA server, I want to authenticate with my SmartCard to FreeIPA server WebUI as a selected role
  • As a user with multiple accounts linked to my Smart Card certificate in FreeIPA server, I want to authenticate with my SmartCard to a desktop system joined to FreeIPA as a selected role
  • As a user with multiple accounts linked to my Smart Card certificate in FreeIPA server, I want to authenticate with my SmartCard to a remote system joined to FreeIPA as a selected role
  • As an administrator, I want to configure SmartCard authentication policy (allow the system to display a prompt for the username when multiple accounts match a single certificate) at the FreeIPA level
  • As an administrator, I want to manage links between a certificate and user accounts (create a link, remove a link, list links for an account, find accounts linked to a certificate), either with the full certificate content or with Subject and Issuer information
  • As an application developer, I want my application using FreeIPA server as authentication backend to enable authentication of users with multiple accounts linked to their SmartCard

Feature Management

The feature will provide 3 different configuration items:

  • the global feature configuration: feature behavior options
  • the rules configuration: each rule will define a scope for the rule (apply to certificates issued by a given issuer), the matching rule (only certificates following some criteria are considered valid for authentication), the mapping rule (the mechanism used to map a certificate to a user), the domains where the user account can be searched, and a boolean to enable/disable the rule
  • the mapping information for a given user

CLI

Configuration

Command Options Description
certmapconfig-mod --promptusername=BOOL Prompt for the username when multiple identities are mapped to a certificate
certmapconfig-show Show the current Certificate Identity Mapping configuration.

Rules

The CLI will allow to define Matching and Mapping rules.

Command Options
certmaprule-{add/mod} RULENAME --desc DESCRIPTION --maprule MAPRULE --matchrule MATCHRULE --domain DOMAIN --priority PRIORITY
certmaprule-enable RULENAME
certmaprule-disable RULENAME
certmaprule-del RULENAME
certmaprule-find RULENAME --rulename=STR --desc STR --maprule STR --matchrule MATCHRULE --domain DOMAIN --priority INT
certmaprule-show RULENAME

All the options are optional.

  • DESCRIPTION: free form text
  • DOMAIN must contain a domain name, either IPA domain name or a trusted AD domain (for instance: ipadomain.com)
  • MAPRULE: the format is described in SSSD / Mapping and sss-certmap(5) man page
  • MATCHRULE: the format is aligned with pkinit_cert_match syntax and described in SSSD / Matching and sss-certmap(5) man page
  • PRIORITY: integer >= 0. The higher the value, the lower the priority. Rules with the same priority will all be considered.

User mapping

The CLI already provides commands related to certificates (ipa user-add, ipa user-mod --certificate and ipa user-{add/remove}-cert). They will be kept when the full certificate needs to be stored in the user entry.


New CLI will allow to link a certificate to a user, with different options:

  • directly with the mapping data
  • through a certificate, from which subject and issuer will be extracted
  • through the certificate subject and issuer
Command Options
user-{add/remove}-certmapdata LOGIN CERTMAPDATA
user-{add/remove}-certmapdata LOGIN --subject SUBJECT --issuer ISSUER
user-{add/remove}-certmapdata LOGIN --certificate BLOB
  • LOGIN
  • CERTMAPDATA will be a free-form text.
  • SUBJECT and ISSUER are DNs (using LDAP ordering) of the certificate subject/issuer
  • BLOB is the base-64 encoded user certificate, from which subject and issuer will be extracted


A new CLI will allow to look for all the users corresponding to the provided certificate:

Command Options
certmap-match FILE
certmap-match --certificate BLOB
  • FILE file containing the certificate
  • BLOB is the base-64 encoded user certificate

The output will contain the matching user names, grouped by domain:

---------------
2 users matched
---------------
  Domain: DOMAIN.EXAMPLE.COM
  Usernames: user1, user2
----------------------------
Number of entries returned 2
----------------------------

UI

  • Add a new tab below "Authentication", with the title "Certificate Identity Mapping"
  • The window will contain 2 sub sections (drop-down menu):
    • Certificate Identity Mapping configuration
    • Certificate Identity Mapping Rules
  • Modify the "User" page to also display "Mapped Certificates" with "Add"/"Delete" buttons

Design

This document concentrates on the management part of the feature (configuration, provisioning of user certificates and mappings). The design for SSSD modifications is out of scope.

High Level schema

The feature will be delivered as a new plugin in FreeIPA and modifications in existing plugins (user, host).

The CLI and GUI tools will write the configuration and mappings in the LDAP backend, thus requiring new schema and permissions/ACIs in order to protect the data.

LDAP

Objectclasses and attributes

The following schema will be used:

attributeTypes: (2.16.840.1.113730.3.8.22.1.1 NAME 'ipaCertMapPromptUsername' DESC 'Prompt for the username when multiple identities are mapped to a certificate' EQUALITY booleanMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.7 SINGLE-VALUE X-ORIGIN 'IPA v4.5' )
attributeTypes: (2.16.840.1.113730.3.8.22.1.2 NAME 'ipaCertMapMapRule' DESC 'Certificate Mapping Rule' SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 SINGLE-VALUE X-ORIGIN 'IPA v4.5' )
attributeTypes: (2.16.840.1.113730.3.8.22.1.3 NAME 'ipaCertMapMatchRule' DESC 'Certificate Matching Rule' SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 SINGLE-VALUE X-ORIGIN 'IPA v4.5' )
attributeTypes: (2.16.840.1.113730.3.8.22.1.4 NAME 'ipaCertMapData' DESC 'Certificate Mapping Data' EQUALITY caseIgnoreMatch SUBSTR caseIgnoreSubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 X-ORIGIN 'IPA v4.5' )
attributeTypes: (2.16.840.1.113730.3.8.22.1.5 NAME 'ipaCertMapPriority' DESC 'Rule priority' SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE X-ORIGIN 'IPA v4.5' )
objectClasses: (2.16.840.1.113730.3.8.22.2.1 NAME 'ipaCertMapConfigObject' DESC 'IPA Certificate Mapping global config options' AUXILIARY MAY ipaCertMapPromptUsername X-ORIGIN 'IPA v4.5' )
objectClasses: (2.16.840.1.113730.3.8.22.2.2 NAME 'ipaCertMapRule' DESC 'IPA Certificate Mapping rule' SUP top STRUCTURAL MUST cn MAY ( description $ ipaCertMapMapRule $ ipaCertMapMatchRule $ associatedDomain $ ipaCertMapPriority $ ipaEnabledFlag ) X-ORIGIN 'IPA v4.5' )
objectClasses: (2.16.840.1.113730.3.8.22.2.3 NAME 'ipaCertMapObject' DESC 'IPA Object for Certificate Mapping' AUXILIARY MAY ipaCertMapData X-ORIGIN 'IPA v4.5' )

Example

dn: cn=certmap,$BASEDN
objectClass: top
objectClass: nsContainer
objectClass: ipaCertMapConfigObject
cn: certmap
ipaCertMapPromptUsername: FALSE
dn: cn=certmaprules,cn=certmap,$BASEDN
objectClass: top
objectClass: nsContainer
cn: certmaprules
dn: cn=rule1,cn=certmaprules,cn=certmap,$BASEDN
cn: rule1
objectClass: ipacertmaprule
associatedDomain: domain.com
ipaCertMapMapRule: (ipacertmapdata=X509:<I>{issuer_dn}<S>{subject_dn})
ipaCertMapPriority: 1
ipaCertMapMatchRule: <ISSUER>CN=Certificate Authority,O=IPA.DEVEL
ipaEnabledFlag: TRUE
description: rule1 description
dn: uid=user1,cn=users,cn=accounts,$BASEDN
objectclass: top
objectclass: (all IPA user objectclasses)
objectclass: ipacertmapobject
ipacertmapdata: X509:<I>CN=Certificate Authority,O=IPA.DEVEL<S>CN=certmaptest.ipa.devel,O=IPA.DEVEL

Access control

New privilege: Certificate Identity Mapping Administrators

New Self-service permission: Users can manage their own X.509 certificate identity mappings

New permissions:

  • System: Read Certmap Configuration: allows to read the configuration in the certmap configuration container
  • System: Modify Certmap Configuration: allows to modify the configuration in the certmap configuration container
  • System: Read Certmap Rules: allows to read the rules in the rules container
  • System: Add Certmap Rules: allows to add new rules in the rules container
  • System: Modify Certmap Rules: allows to modify rules in the rules container
  • System: Delete Certmap Rules: allows to delete rules in the rules container
  • System: Manage User Certificate Mappings: allow to add/remove a certificate identity mapping to a user


The System: Read Certmap Configuration and System: Read Certmap Rules permissions will be granted to ldap:///all, and all the other permissions will be added to the Certificate Identity Mapping Administrators privilege.

Implementation

Upgrade

The upgrade needs to install the new schema and create the entry cn=certmap,cn=ipa,cn=etc,$BASEDN and the container entry cn=certmaprules,cn=certmap,cn=ipa,cn=etc,$BASEDN.

In prevision of future modifications, the configuration cn=certmap,cn=ipa,cn=etc,$BASEDN will contain a ipacertmapversion attribute.

How to Use

  • Allow to display the prompt for username disambiguation
ipa certmapconfig-mod --promptusername=TRUE
  • Define a mapping rule based on subject and issuer
ipa certmaprule-add defaultrule --desc "Default mapping rule" --maprule "(ipacertmapdata=X509:<I>{issuer_dn}<S>{subject_dn})"
  • Configure the mapping between the user testuser and a certificate issued by cn=extca,dc=example,dc=com with subject cn=myname,dc=example,dc=com
ipa user-add-certmap testuser --subject cn=myname,dc=example,dc=com --issuer cn=extca,dc=example,dc=com

or

ipa user-add-certmap testuser --data "X509:<I>cn=extca,dc=example,dc=com<S>cn=myname,dc=example,dc=com"
  • On an enrolled client, login to GDM using a smart card containing the user cert. The authenticate user will be "testuser"

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.

Troubleshooting

Please check FreeIPA: Troubleshooting SmartCard authentication blog post for tips.