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Chapter 18. Using the KDC Proxy in IdM

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Some administrators might choose to make the default Kerberos ports inaccessible in their deployment. To allow users, hosts, and services to obtain Kerberos credentials, you can use the HTTPS service as a proxy that communicates with Kerberos via the HTTPS port 443.

In Identity Management (IdM), the Kerberos Key Distribution Center Proxy (KKDCP) provides this functionality.

On an IdM server, KKDCP is enabled by default and available at https://server.idm.example.com/KdcProxy. On an IdM client, you must change its Kerberos configuration to access the KKDCP.

18.1. Configuring an IdM client to use KKDCP

As an Identity Management (IdM) system administrator, you can configure an IdM client to use the Kerberos Key Distribution Center Proxy (KKDCP) on an IdM server. This is useful if the default Kerberos ports are not accessible on the IdM server and the HTTPS port 443 is the only way of accessing the Kerberos service.

Prerequisites

  • You have root access to the IdM client.

Procedure

  1. Open the /etc/krb5.conf file for editing.
  2. In the [realms] section, enter the URL of the KKDCP for the kdc, admin_server, and kpasswd_server options:

    [realms]
    EXAMPLE.COM = {
      kdc = https://kdc.example.com/KdcProxy
      admin_server = https://kdc.example.com/KdcProxy
      kpasswd_server = https://kdc.example.com/KdcProxy
      default_domain = example.com
    }

    For redundancy, you can add the parameters kdc, admin_server, and kpasswd_server multiple times to indicate different KKDCP servers.

  3. Restart the sssd service to make the changes take effect:

    ~]# systemctl restart sssd

18.2. Verifying that KKDCP is enabled on an IdM server

On an Identity Management (IdM) server, the Kerberos Key Distribution Center Proxy (KKDCP) is automatically enabled each time the Apache web server starts if the attribute and value pair ipaConfigString=kdcProxyEnabled exists in the directory. In this situation, the symbolic link /etc/httpd/conf.d/ipa-kdc-proxy.conf is created.

You can verify if the KKDCP is enabled on the IdM server, even as an unprivileged user.

Procedure

  • Check that the symbolic link exists:
$ ls -l /etc/httpd/conf.d/ipa-kdc-proxy.conf
lrwxrwxrwx. 1 root root 36 Jun 21  2020 /etc/httpd/conf.d/ipa-kdc-proxy.conf -> /etc/ipa/kdcproxy/ipa-kdc-proxy.conf

The output confirms that KKDCP is enabled.

18.3. Disabling KKDCP on an IdM server

As an Identity Management (IdM) system administrator, you can disable the Kerberos Key Distribution Center Proxy (KKDCP) on an IdM server.

Prerequisites

  • You have root access to the IdM server.

Procedure

  1. Remove the ipaConfigString=kdcProxyEnabled attribute and value pair from the directory:

    # ipa-ldap-updater /usr/share/ipa/kdcproxy-disable.uldif
    Update complete
    The ipa-ldap-updater command was successful
  2. Restart the httpd service:

    # systemctl restart httpd.service

KKDCP is now disabled on the current IdM server.

Verification steps

  • Verify that the symbolic link does not exist:

    $ ls -l /etc/httpd/conf.d/ipa-kdc-proxy.conf
    ls: cannot access '/etc/httpd/conf.d/ipa-kdc-proxy.conf': No such file or directory

18.4. Re-enabling KKDCP on an IdM server

On an IdM server, the Kerberos Key Distribution Center Proxy (KKDCP) is enabled by default and available at https://server.idm.example.com/KdcProxy.

If KKDCP has been disabled on a server, you can re-enable it.

Prerequisites

  • You have root access to the IdM server.

Procedure

  1. Add the ipaConfigString=kdcProxyEnabled attribute and value pair to the directory:

    # ipa-ldap-updater /usr/share/ipa/kdcproxy-enable.uldif
    Update complete
    The ipa-ldap-updater command was successful
  2. Restart the httpd service:

    # systemctl restart httpd.service

KKDCP is now enabled on the current IdM server.

Verification steps

  • Verify that the symbolic link exists:

    $ ls -l /etc/httpd/conf.d/ipa-kdc-proxy.conf
    lrwxrwxrwx. 1 root root 36 Jun 21  2020 /etc/httpd/conf.d/ipa-kdc-proxy.conf -> /etc/ipa/kdcproxy/ipa-kdc-proxy.conf

18.5. Configuring the KKDCP server I

With the following configuration, you can enable TCP to be used as the transport protocol between the IdM KKDCP and the Active Directory (AD) realm, where multiple Kerberos servers are used.

Prerequisites

  • You have root access.

Procedure

  1. Set the use_dns parameter in the [global] section of the /etc/ipa/kdcproxy/kdcproxy.conf file to false.

    [global]
    use_dns = false
  2. Put the proxied realm information into the /etc/ipa/kdcproxy/kdcproxy.conf file. For example, for the [AD.EXAMPLE.COM] realm with proxy list the realm configuration parameters as follows:

    [AD.EXAMPLE.COM]
    kerberos = kerberos+tcp://1.2.3.4:88 kerberos+tcp://5.6.7.8:88
    kpasswd = kpasswd+tcp://1.2.3.4:464 kpasswd+tcp://5.6.7.8:464
    Important

    The realm configuration parameters must list multiple servers separated by a space, as opposed to /etc/krb5.conf and kdc.conf, in which certain options may be specified multiple times.

  3. Restart Identity Management (IdM) services:

    # ipactl restart

Additional resources

18.6. Configuring the KKDCP server II

The following server configuration relies on the DNS service records to find Active Directory (AD) servers to communicate with.

Prerequisites

  • You have root access.

Procedure

  1. In the /etc/ipa/kdcproxy/kdcproxy.conf file, the [global] section, set the use_dns parameter to true.

    [global]
    configs = mit
    use_dns = true

    The configs parameter allows you to load other configuration modules. In this case, the configuration is read from the MIT libkrb5 library.

  2. Optional: In case you do not want to use DNS service records, add explicit AD servers to the [realms] section of the /etc/krb5.conf file. If the realm with proxy is, for example, AD.EXAMPLE.COM, you add:

    [realms]
    AD.EXAMPLE.COM = {
        kdc = ad-server.ad.example.com
        kpasswd_server = ad-server.ad.example.com
    }
  3. Restart Identity Management (IdM) services:

    # ipactl restart

Additional resources

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