Authselect_migration

Authselect_migration#

Overview#

authselect is a new tool to configure authentication sources on a system. It is going to replace authconfig in the future (see the page for Authselect on Fedora wiki). Since IPA is dependent on authconfig, it is required to extend its functionality so authselect can be used when it is available. Authselect will be a default tool in Fedora 28, authconfig command will still be available (provided by the authselect-compat package) but its functionality will be limited.

The major difference between authconfig and authselect is the use of a configuration profile: authselect provides pre-defined profiles that can be tuned by enabling specific features. The available profiles can be found using authselect list and their features with authselect show PROFILE-ID. For instance, the sssd profile accepts the features with-mkhomedir or with-smartcard, and the winbind profile accepts the feature with-mkhomedir but not with-smartcard.

Current implementation#

This section lists the components of FreeIPA that are currently relying on authconfig.

Package dependency#

FreeIPA currently has a dependency on authconfig package (freeipa-client package).

Client installation#

Currently authconfig is triggered during client install to:

  • configure NIS. the commands below is used

`` authconfig –nisdomain=``

  • with sssd (default).

To enable SSSD for user information and authentication:

`` authconfig –enablesssd –enablesssdauth``

To enable kerberos authentication:

`` authconfig –enablekrb5 –nostart``

  • no_sssd (deprecated).

To enable LDAP for user information:

`` authconfig –enableldap –enableforcelegacy``

The following ipa-client-install options have an impact on authentication configuration:

  • –nisdomain=NISDOMAIN: Set the NIS domain name as specified. By default, this is set to the IPA domain name.

  • –no-nisdomain: Do not configure NIS domain name.

  • –no-sssd: Do not configure the client to use SSSD for authentication, use nss_ldap instead.

  • –noac: Do not use Authconfig to modify the nsswitch.conf and PAM configuration.

Note that the ipa client code is using the tasks package to call distribution-specific code: only the fedora-like distributions use authconfig, other distributions must implement their own routines to configure the authentication mechanisms.

Backup/restore#

The commands ipa-backup and ipa-restore both need to save/restore the current configuration. ipa-backup is calling:

`` authconfig –savebackup ``

and saves the content of the backup directory in the backup file. ipa-restore is calling

`` authconfig –restorebackup ``

to restore the saved configuration.

ipa-advise plugins#

ipa-advise command provides configuration advices for various use cases. For instance, ipa-advise config-server-for-smart-card-auth produces a shell script that can be executed in order to configure the server to allow Smart Card authentication. Some of the plugins produce shell scripts that are calling authconfig:

  • ipa-advise config-client-for-smart-card-auth: Instructions for enabling Smart Card authentication on a single FreeIPA client.

  • ipa-advise config-fedora-authconfig: Authconfig instructions for configuring Fedora 18/19 client with IPA server without use of SSSD.

  • ipa-advise config-redhat-sssd-before-1-9: Instructions for configuring a system with an old version of SSSD (1.5-1.8) as a FreeIPA client.

  • ipa-advise config-redhat-nss-pam-ldapd: Instructions for configuring a system with nss-pam-ldapd as a FreeIPA client.

  • ipa-advise config-redhat-nss-ldap: Instructions for configuring a system with nss-ldap as a FreeIPA client.

Design#

General decisions#

  • As authselect may not be available on all distributions, we need to keep the same strategy as implemented by the current code: rely on the tasks package to have distribution-specific code. FreeIPA team will provide code for fedora-like distributions, based on authselect and the other distributions should not be disturbed by the changes.

  • Authselect-compat package provides an equivalent to authconfig, with a compatibility layer for some options and deprecating other options. Because of these deprecated options, it does not seem safe enough to keep on using authconfig tool and the choice is made to completely switch to using authselect. This implies that the dependency on authconfig will be completely removed and replaced with a dependency on authselect. Note that we will not have any dependency on authselect-compat, meaning that FreeIPA code should not rely any more on authconfig command.

  • It seems obvious to state that FreeIPA will use the sssd profile but this has major consequences. Previously, it was possible to install a client with –no-sssd or –noac options, but it will not be possible any more for new client installations on fedora-based distributions.

New client installation#

Currently, the algorithm for PAM stack configuration is the following:

authconfig --nisdomain=<domain>
if (sssd) then
   authconfig --enablesssd --enablesssdauth
else
   authconfig --enableldap --enableforcelegacy --enablekrb5 --nostart
done
if (mkhomedir) then
   authconfig --enablemkhomedir
done

–no-sssd and –noac options#

With the migration to authselect and the choice of using sssd profile, we will now refuse the –no-sssd and -noac options for fedora-based distributions. This can be achieved by adding a tasks method (i.e. with a distribution-specific implementation) is_nosssd_supported(), and a check in the client installer that refuses the option in case is_nosssd_supported returns False.

PAM stack configuration#

Calls to the authconfig tool are completely replaced by calls to authselect, picking the sssd profile. PAM configuration steps are moved into a separate class following bridge oop pattern. All related code is under ipaplatform/redhat/authconfig.py, ensuring that only fedora-based distributions are impacted by the modifications.

–mkhomedir option#

The homedir creation can also be enabled with authselect with: authselect select sssd with-mkhomedir.

NIS domain configuration#

Authconfig is currently used in the client installer to configure the NIS domain. It is also possible to configure the NIS domain without a call to authconfig tool, by direct modification of a config file. This is the chosen approach: append (or replace) the NISDOMAIN=value line in the file /etc/sysconfig/network.

Client uninstallation#

The client uninstallation needs to revert the system to the same state as before client install. In order to do this, the client installation will store the profile used pre-installation in the system store (/var/lib/ipa-client/sysrestore/sysrestore.state) with the following format:

[authselect]
profile=
features_list=

Profile and features_list will be used to revert to the previous state during uninstallation.

Note: When the client was installed with the authconfig tool, the system store does not contain this information. In this case, the uninstaller will simply warn that it is not able to revert to the exact state before installation and will apply the default authselect profile, namely the sssd profile without any feature.

New server installation#

The server-specific install code is not impacted by this migration (only the client-part of the installation is).

Backup and restore#

Backup#

The authselect tool offers the “current” command to retrieve the current configuration (profile and enabled features). For instance:

$ authselect current --raw
sssd with-mkhomedir

The ipa-backup command needs to use this command to save the current configuration inside a new file in the backup directory.

Restore#

Note: only full restore is impacted by this feature. Data-only restore does not touch the authentication configuration.

The ipa-restore command needs to read the saved configuration from the backup directory and re-apply the same configuration using

`` $ authselect select \ `` ``\ `` --force

Note: if the backup was done on a server *before* the migration to authselect, the ipa-restore will detect that restore is trying to restore data from a different release and prompt for user confirmation with a warning. Unattended restore will fail.

ipa-advise plugins#

config-client-for-smart-card-auth plugin#

This plugin configures a FreeIPA client for smart card authentication. Instead of calling

`` authconfig –enablesssd –enablesssdauth –enablesmartcard ‘ ‘–smartcardmodule=sssd –smartcardaction=1 –updateall``

the plugin must use

`` authselect enable-feature with-smartcard``

config-fedora-authconfig plugin#

This plugin configures Fedora 18/19 client without the use of sssd. These versions are not suppported any more and the plugin can be dropped.

other plugins#

The other plugins (config-redhat-sssd-before-1-9, config-redhat-nss-pam-ldapd and config-redhat-nss-ldap) are related to RHEL 5, where authselect will not be available. The scripts produced by ipa-advise can be generated on a recent FreeIPA server and run on a RHEL5 system, meaning that we can keep them.

Upgrade#

Migration for older clients#

Client upgrade will not modify the configuration since the PAM stack configuration is already in place.

Migration for older servers#

The server has to be migrated to authselect to make sure that backup and restore code works properly for new servers and also for older servers. If no migration was implemented, this would imply that backup/restore code must be able to handle 2 different types of configurations (with authconfig or with authselect), leading to a maintenance nightmare. Because of this, the choice is made to migrate the configuration to an authselect profile during the upgrade.

The ipa-server-upgrade tool will perform the migration to an authselect profile. It needs to take care of the following points:

  • check if the server was initially installed with the flag –mkhomedir (by reading the content of the system store). In this case, the sssd profile with enable-mkhomedir option must be selected. Otherwise use the sssd profile without the option.

  • update the configuration backed up in the system store (/var/lib/ipa-client/sysrestore/sysrestore.state). The system store may contain

[authconfig]
mkhomedir=...
ldap=...
krb5=...
sssd=...
sssdauth=...

and this would have to be replaced with

[authselect]
profile=sssd
mkhomedir=...

Use cases#

As this migration is mainly internal, it will not modify the interfaces as seen by a user or system administrator, except for the use of –no-sssd or –noac options in ipa-client-install (which will now be refused on fedora-based distributions).

A careful user may notice the presence of a new directory /etc/authselect created during the authselect package installation, containing /etc/authselect/authselect.conf file storing the current profile and features:

$ cat /etc/authselect/authselect.conf
sssd

Testing#

The tests need to focus on 2 main parts, new installations and upgrades. They can be run on fedora-based distributions.

Upgrade#

  • upgrade must keep the mkhomedir flag (if the server was installed with –mkhomedir, then the authselect config obtained after upgrade must also have this option)

  • backup and restore must still be working after the upgrade

  • uninstall must still be working after the upgrade (potentially with a warning if the client was installed with authconfig).

New installations#

  • new client installation must install the sssd profile, with or without the with-mkhomedir feature (depending on the presence of –mkhomedir flag)

  • ipa-client-install must refuse the –no-sssd and –noac options with a meaningful error message

  • client install / uninstall must revert to the previous authselect profile

  • new server installation must install the sssd profile, with or without the with-mkhomedir feature (depending on the presence of –mkhomedir flag)

  • backup/restore must work with a new server installation

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