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Setting Up Percona PAM with Active Directory for External Authentication

 | July 13, 2017 |  Posted In: MySQL, Percona Server, Security, SSL

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Percona PAMIn this blog post, we’ll look at how to set up Percona PAM with Active Directory for external authentication.

In my previous article on Percona PAM, I demonstrated how to use Samba as a domain, and how easy it is to create domain users and groups via the samba-tool. Then we configured nss-pam-ldapd and nscd to enumerate user and group information via LDAP calls, and authenticate users from this source.

This time around, I will demonstrate two other ways of using Active Directory for external authentication by joining the domain via SSSD or Winbind. System Security Services Daemon (SSSD) allows you to configure access to several authentication hosts such as LDAP, Kerberos, Samba and Active Directory and have your system use this service for all types of lookups. Winbind, on the other hand, pulls data from Samba or Active Directory only. If you’re mulling over using SSSD or Winbind, take a look at this article on what SSSD or Winbind support.

For both methods, we’ll use realmd. That makes it easy to join a domain and enumerate users from it.

My testbed environment consists of two machines:

Samba PDC
OS: CentOS 7
IP Address: 172.16.0.10
Hostname: samba-10.example.com
Domain name: EXAMPLE.COM
DNS: 8.8.8.8(Google DNS), 8.8.4.4(Google DNS), 172.16.0.10(Samba)
Firewall: none

Note: Please follow the steps in the last article for setting up the Samba PDC environment.

Percona Server 5.7 with LDAP authentication via SSS or WinBind
OS: CentOS 7
IP Address: 172.16.0.21
Hostname: ps-ldap-21.example.com
DNS: 172.16.0.10(Samba PDC)

Installing realmd and Its Dependencies

  1. First, we need to make sure that the time is in sync (since this is a requirement for joining domains). Install NTP and make sure that it starts up at boot time:
  2. Install realmd and its dependencies for SSSD or Winbind.
    For SSSD:

    For Winbind:

Joining the Domain via SSSD and Preparing It for Percona PAM

  1. Run realm discover domain for realmd to discover what type of server it’s connecting to and what packages dependencies need to be installed:

    Our Samba PDC is detected as an Active Directory Controller, and the packages required have been installed previously.
  2. The next step is to join the domain by running realm join domain. If you want to get more information, add the --verbose option. You could also add the -U user option if you want to use a different administrator account.

    As you can see from the command above, the realm command simplifies SSSD configuration and uses existing tools such as net and authconfig to join the domain and use it as an identity provider.
  3. Let’s test if we enumerate existing accounts by using the id command:

    As you can see, the user can be queried if the domain is specified. So if you want to log in as ‘jervin@example.com’, in Percona Server for MySQL you’ll need to create the user as ‘jervin@example.com’ and not ‘jervin’. For example:

    If you want to omit the domain name when logging in, you’ll need to replace “use_fully_qualified_names = True” to “use_fully_qualified_names = False” in /etc/sssd/sssd.conf, and then restart SSSD. If you do this, then the user can be found without providing the domain:

    When you create the MySQL user, you don’t need to include the domain anymore:
  4. Optionally, you can specify which users and groups can log in by adding these settings to SSSD:
    Domain access filter
    Under “[domain/example.com]” /etc/sssd/sssd.conf, you can add the following to specify that only users that are members of support and dba are allowed to use SSSD. For example:

    Simple filters
    You can use realm permit or realm permit -g to allow particular users or groups. For example:

    You can check sssd.conf on how these ACLs are implemented:
  5. Finally, configure Percona Server for MySQL to authenticate to SSSD by creating /etc/pam.d/mysqld with this content:
  6. Done. All you need to do now is to install Percona Server for MySQL, enable the auth_pam and auth_pam_compat plugins, and add PAM users. You can then check for authentication errors at /var/log/secure for troubleshooting. You could also get verbose logs by adding debug_level=[1-9] to [nss], [pam], or [domain] and then restarting SSSD. You can view the logs from /var/log/sssd.

Joining the Domain via Winbind and Preparing it for Percona PAM

  1. The realm command assumes that SSSD is used. To change the client software, use --client-software=winbind instead:
  2. Since the required packages have already been installed, we can now attempt to join this host to the domain:
  3. Let’s test if we enumerate existing accounts by using the id command

    Unfortunately for Winbind, users identified with their domains cannot login to Percona Server for MySQL. We need to disable this from the Samba config (performed in the next step).
  4. Edit /etc/samba/smb.conf, and change “winbind use default domain = no” to “winbind use default domain = yes”. Restart the Winbind service. For example:

    Try running id again:

    When you create the MySQL user, do not include the domain name. For example:
  5. Finally, configure Percona Server for MySQL to authenticate to Winbind by creating /etc/pam.d/mysqld with this content:

You can debug authentication attempts by reviewing the logs at /var/log/secure. You may also change “auth required pam_winbind.so” to “auth required pam_winbind.so debug” in /etc/pam.d/mysqld to get verbose logging in the same file.

As for filtering who can authenticate with Winbind, you can add require_membership_of=group_name under the [global] section of /etc/security/pam_winbind.conf

You’ll need to restart winbind daemon to apply the changes.

Conclusion

Thanks to realmd, it’s easier to setup Active Directory as an identity provider. With minimal configuration tweaks, you can use the identity provider to authenticate MySQL users.

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Jaime Sicam

Jaime is a Senior Technical Services Engineer at Percona. Prior to joining Percona, Jaime worked as a remote system administrator managing high-traffic websites and consultant for several local companies. He also conducted Linux trainings in several schools. Jaime is based in the Philippines. He enjoys road trips and photography in his spare time.

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