Jul
13
2017
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Setting Up Percona PAM with Active Directory for External Authentication

Percona PAM

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: 
    [root@ps-ldap-21 ~]# yum -y install ntp
* * *
Installed:
ntp.x86_64 0:4.2.6p5-25.el7.centos.2
* * *
[root@ps-ldap-21 ~]# ntpdate 0.centos.pool.ntp.org
systemctl enable ntpd.service
systemc 3 Jul 03:48:35 ntpdate[3708]: step time server 202.90.132.242 offset 1.024550 sec
[root@ps-ldap-21 ~]# systemctl enable ntpd.service
Created symlink from /etc/systemd/system/multi-user.target.wants/ntpd.service to /usr/lib/systemd/system/ntpd.service.
[root@ps-ldap-21 ~]# systemctl start ntpd.service
  2. Install realmd and its dependencies for SSSD or Winbind.
    For SSSD:

    yum -y install realmd oddjob oddjob-mkhomedir sssd adcli samba-common-tools

    For Winbind:

    yum -y install realmd oddjob oddjob-mkhomedir samba-winbind-clients samba-winbind samba-common-tools

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: 
    [root@ps-ldap-21 ~]# realm discover example.com
example.com
type: kerberos
realm-name: EXAMPLE.COM
domain-name: example.com
configured: no
server-software: active-directory
client-software: sssd
required-package: oddjob
required-package: oddjob-mkhomedir
required-package: sssd
required-package: adcli
required-package: samba-common-tools

    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.

    [root@ps-ldap-21 ~]# realm join example.com --verbose
 * Resolving: _ldap._tcp.example.com
 * Performing LDAP DSE lookup on: 172.16.0.10
 * Successfully discovered: example.com
Password for Administrator:
 * Required files: /usr/sbin/oddjobd, /usr/libexec/oddjob/mkhomedir, /usr/sbin/sssd, /usr/bin/net
 * LANG=C LOGNAME=root /usr/bin/net -s /var/cache/realmd/realmd-smb-conf.DM6W2Y -U Administrator ads join example.com
Enter Administrator's password:
Using short domain name -- EXAMPLE
Joined 'PS-LDAP-21' to dns domain 'example.com'
 * LANG=C LOGNAME=root /usr/bin/net -s /var/cache/realmd/realmd-smb-conf.DM6W2Y -U Administrator ads keytab create
Enter Administrator's password:
 * /usr/bin/systemctl enable sssd.service
Created symlink from /etc/systemd/system/multi-user.target.wants/sssd.service to /usr/lib/systemd/system/sssd.service.
 * /usr/bin/systemctl restart sssd.service
 * /usr/bin/sh -c /usr/sbin/authconfig --update --enablesssd --enablesssdauth --enablemkhomedir --nostart && /usr/bin/systemctl enable oddjobd.service && /usr/bin/systemctl start oddjobd.service
 * Successfully enrolled machine in realm

    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:

    [root@ps-ldap-21 ~]# id jervin
id: jervin: no such user
[root@ps-ldap-21 ~]# id jervin@example.com
uid=343401115(jervin@example.com) gid=343400513(domain users@example.com) groups=343400513(domain users@example.com),343401103(support@example.com)

    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:

    # Creating user 'jervin@example.com'
CREATE USER 'jervin@example.com'@'%' IDENTIFIED WITH auth_pam;
# Logging in as 'jervin@example.com'
mysql -u 'jervin@example.com'

    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:

    [root@ps-ldap-21 ~]# id jervin
uid=343401115(jervin) gid=343400513(domain users) groups=343400513(domain users),343401103(support)
[root@ps-ldap-21 ~]# id jervin@example.com
uid=343401115(jervin) gid=343400513(domain users) groups=343400513(domain users),343401103(support)

    When you create the MySQL user, you don’t need to include the domain anymore:

    # Creating user 'jervin'
CREATE USER 'jervin'@'%' IDENTIFIED WITH auth_pam;
# Logging in as 'jervin'
mysql -u jervin
  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:

    ad_access_filter = (|(memberOf=CN=dba,CN=Users,DC=example,DC=com)(memberOf=CN=support,CN=Users,DC=example,DC=com))

    Simple filters
    You can use 

    realm permit

     or 

    realm permit -g

     to allow particular users or groups. For example:

    realm permit jervin
realm permit -g support
realm permit -g dba

    You can check sssd.conf on how these ACLs are implemented:

    access_provider = simple
simple_allow_groups = support, dba
simple_allow_users = jervin
  5. Finally, configure Percona Server for MySQL to authenticate to SSSD by creating /etc/pam.d/mysqld with this content: 
    auth required pam_sss.so
account required pam_sss.so
  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:

    [root@ps-ldap-21 ~]# realm --client-software=winbind discover example.com
example.com
    type: kerberos
    realm-name: EXAMPLE.COM
    domain-name: example.com
    configured: no  
    server-software: active-directory
    client-software: winbind
    required-package: oddjob-mkhomedir
    required-package: oddjob
    required-package: samba-winbind-clients
    required-package: samba-winbind
    required-package: samba-common-tools
  2. Since the required packages have already been installed, we can now attempt to join this host to the domain: 
    [root@ps-ldap-21 ~]# realm --verbose --client-software=winbind join example.com
 * Resolving: _ldap._tcp.example.com
 * Performing LDAP DSE lookup on: 172.16.0.10
 * Successfully discovered: example.com
Password for Administrator:
 * Required files: /usr/libexec/oddjob/mkhomedir, /usr/sbin/oddjobd, /usr/bin/wbinfo, /usr/sbin/winbindd, /usr/bin/net
 * LANG=C LOGNAME=root /usr/bin/net -s /var/cache/realmd/realmd-smb-conf.9YEO2Y -U Administrator ads join example.com
Enter Administrator's password:
Using short domain name -- EXAMPLE
Joined 'PS-LDAP-21' to dns domain 'example.com'
 * LANG=C LOGNAME=root /usr/bin/net -s /var/cache/realmd/realmd-smb-conf.9YEO2Y -U Administrator ads keytab create
Enter Administrator's password:
 * /usr/bin/systemctl enable winbind.service
Created symlink from /etc/systemd/system/multi-user.target.wants/winbind.service to /usr/lib/systemd/system/winbind.service.
 * /usr/bin/systemctl restart winbind.service
 * /usr/bin/sh -c /usr/sbin/authconfig --update --enablewinbind --enablewinbindauth --enablemkhomedir --nostart && /usr/bin/systemctl enable oddjobd.service && /usr/bin/systemctl start oddjobd.service
 * Successfully enrolled machine in realm
  3. Let’s test if we enumerate existing accounts by using the 
    id

     command

    [root@ps-ldap-21 ~]# id jervin
id: jervin: no such user
[root@ps-ldap-21 ~]# id jervin@example.com
uid=10000(EXAMPLEjervin) gid=10000(EXAMPLEdomain users) groups=10000(EXAMPLEdomain users),10001(EXAMPLEsupport)

    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: 
    vi /etc/samba/smb.conf
#Look for:
"winbind use default domain = no"
#Change to:
"winbind use default domain = yes"
systemctl restart winbind.service

    Try running 

    id

     again:

    [root@ps-ldap-21 ~]# id jervin
uid=10000(jervin) gid=10000(domain users) groups=10000(domain users),10001(support)
[root@ps-ldap-21 ~]# id jervin@example.com
id: jervin@example.com: no such user

    When you create the MySQL user, do not include the domain name. For example:

    # Creating user 'jervin'
CREATE USER 'jervin'@'%' IDENTIFIED WITH auth_pam;
# Logging in as 'jervin'
mysql -u jervin
  5. Finally, configure Percona Server for MySQL to authenticate to Winbind by creating /etc/pam.d/mysqld with this content: 
    auth required pam_winbind.so
account required pam_winbind.so

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.

Written by in: MySQL,Percona PAM,percona server,Percona Server for MySQL,realmd,SSSD,Winbind,Zend Developer | Tags: ,

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