Chapter 7. Configuring a RHEL host to use AD as an authentication provider

Procedure

1. Create the AD_user user account locally without assigning a password to it:

   # useradd AD_user

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2. Open the /etc/nsswitch.conf file for editing, and make sure that it contains the following lines:

   passwd:     sss files systemd
   group:      sss files systemd
   shadow:     files sss

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3. Open the /etc/krb5.conf file for editing, and make sure that it contains the following sections and items:

   # To opt out of the system crypto-policies configuration of krb5, remove the
   # symlink at /etc/krb5.conf.d/crypto-policies which will not be recreated.
   includedir /etc/krb5.conf.d/
   
   [logging]
       default = FILE:/var/log/krb5libs.log
       kdc = FILE:/var/log/krb5kdc.log
       admin_server = FILE:/var/log/kadmind.log
   
   [libdefaults]
       dns_lookup_realm = false
       ticket_lifetime = 24h
       renew_lifetime = 7d
       forwardable = true
       rdns = false
       pkinit_anchors = /etc/pki/tls/certs/ca-bundle.crt
       spake_preauth_groups = edwards25519
       default_realm = EXAMPLE.COM
       default_ccache_name = KEYRING:persistent:%{uid}
   
   [realms]
    EXAMPLE.COM = {
        kdc = ad.example.com
        admin_server = ad.example.com
    }
   
   [domain_realm]
    .example.com = EXAMPLE.COM
    example.com = EXAMPLE.COM

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4. Create the /etc/sssd/sssd.conf file and insert the following sections and lines into it:

   [sssd]
       services = nss, pam
       domains = EXAMPLE.COM
   
   [domain/EXAMPLE.COM]
       id_provider = proxy
       proxy_lib_name = files
       auth_provider = krb5
       krb5_realm = EXAMPLE.COM
       krb5_server = ad.example.com

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5. Change the permissions on the /etc/sssd/sssd.conf file:

   # chmod 600 /etc/sssd/sssd.conf

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6. Start the Security System Services Daemon (SSSD):

   # systemctl start sssd

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7. Enable SSSD:

   # systemctl enable sssd

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8. Open the /etc/pam.d/system-auth file, and modify it so that it contains the following sections and lines:

   # Generated by authselect on Wed May  8 08:55:04 2019
   # Do not modify this file manually.
   
   auth        required                                     pam_env.so
   auth        required                                     pam_faildelay.so delay=2000000
   auth        [default=1 ignore=ignore success=ok]         pam_succeed_if.so uid >= 1000 quiet
   auth        [default=1 ignore=ignore success=ok]         pam_localuser.so
   auth        sufficient                                   pam_unix.so nullok try_first_pass
   auth        requisite                                    pam_succeed_if.so uid >= 1000 quiet_success
   auth        sufficient                                   pam_sss.so forward_pass
   auth        required                                     pam_deny.so
   
   account     required                                     pam_unix.so
   account     sufficient                                   pam_localuser.so
   account     sufficient                                   pam_succeed_if.so uid < 1000 quiet
   account     [default=bad success=ok user_unknown=ignore] pam_sss.so
   account     required                                     pam_permit.so
   
   password    requisite                                    pam_pwquality.so try_first_pass local_users_only
   password    sufficient                                   pam_unix.so sha512 shadow nullok try_first_pass use_authtok
   password    sufficient                                   pam_sss.so use_authtok
   password    required                                     pam_deny.so
   
   session     optional                                     pam_keyinit.so revoke
   session     required                                     pam_limits.so
   -session    optional                                     pam_systemd.so
   session     [success=1 default=ignore]                   pam_succeed_if.so service in crond quiet use_uid
   session     required                                     pam_unix.so
   session     optional                                     pam_sss.so

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9. Copy the contents of the /etc/pam.d/system-auth file into the /etc/pam.d/password-auth file. Enter yes to confirm the overwriting of the current contents of the file:

   # cp /etc/pam.d/system-auth /etc/pam.d/password-auth
   cp: overwrite '/etc/pam.d/password-auth'? yes

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Verification

1. Request a Kerberos ticket-granting ticket (TGT) for AD_user. Enter the password of AD_user as requested:

   # kinit AD_user
   Password for AD_user@EXAMPLE.COM:

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2. Display the obtained TGT:

   # klist
   Ticket cache: KEYRING:persistent:0:0
   Default principal: AD_user@EXAMPLE.COM
   
   Valid starting     Expires            Service principal
   11/02/20 04:16:38  11/02/20 14:16:38  krbtgt/EXAMPLE.COM@EXAMPLE.COM
   	renew until 18/02/20 04:16:34

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