Chapter 50. Managing Kerberos ticket policies

Identity Management’s authentication mechanisms use the Kerberos infrastructure established by the Key Distribution Center (KDC). The KDC is the trusted authority that stores credential information and ensures the authenticity of data originating from entities within the IdM network.

Each IdM user, service, and host acts as a Kerberos client and is identified by a unique Kerberos principal:

The following image is a simplification of the communication between a Kerberos client, the KDC, and a Kerberized application that the client wants to communicate with.

IdM Kerberos ticket policies implement the following ticket policy types:

The Kerberos Key Distribution Center (KDC) attaches authentication indicators to a ticket-granting ticket (TGT) based on which pre-authentication mechanism the client used to prove its identity:

The KDC then attaches the authentication indicators from the TGT to any service ticket requests that stem from it. The KDC enforces policies such as service access control, maximum ticket lifetime, and maximum renewable age based on the authentication indicators.

For example, to require two-factor authentication to connect to a Virtual Private Network (VPN), associate the otp authentication indicator with that service. Only users who used a One-Time password to obtain their initial TGT from the KDC will be able to log in to the VPN:

Figure 50.1. Example of a VPN service requiring the otp authentication indicator

If a service or a host has no authentication indicators assigned to it, it will accept tickets authenticated by any mechanism.

The authentication mechanisms supported by Identity Management (IdM) vary in their authentication strength. For example, obtaining the initial Kerberos ticket-granting ticket (TGT) using a one-time password (OTP) in combination with a standard password is considered more secure than authentication using only a standard password.

By associating authentication indicators with a particular IdM service, you can, as an IdM administrator, configure the service so that only users who used those specific pre-authentication mechanisms to obtain their initial ticket-granting ticket (TGT) will be able to access the service.

In this way, you can configure different IdM services so that:

Figure 50.2. Example of authenticating using different technologies

This procedure describes creating an IdM service and configuring it to require particular Kerberos authentication indicators from incoming service ticket requests.

host/server.example.com@EXAMPLE.COM
HTTP/server.example.com@EXAMPLE.COM
ldap/server.example.com@EXAMPLE.COM
DNS/server.example.com@EXAMPLE.COM
cifs/server.example.com@EXAMPLE.COM

[root@server ~]# ipa service-mod testservice/client.example.com@EXAMPLE.COM --auth-ind ''
------------------------------------------------------
Modified service "testservice/client.example.com@EXAMPLE.COM"
------------------------------------------------------
  Principal name: testservice/client.example.com@EXAMPLE.COM
  Principal alias: testservice/client.example.com@EXAMPLE.COM
  Managed by: client.example.com

[root@server ~]# kdestroy

The global ticket policy applies to all service tickets and to users that do not have any per-user ticket policies defined.

The following procedure describes adjusting the maximum ticket lifetime and maximum ticket renewal age for the global Kerberos ticket policy using the ipa krbtpolicy-mod command.

While using the ipa krbtpolicy-mod command, specify at least one of the following arguments:

Follow this procedure to adjust the global maximum ticket lifetime and maximum renewable age for each authentication indicator. These settings apply to users that do not have per-user ticket policies defined.

Use the ipa krbtpolicy-mod command to specify the global maximum lifetime or maximum renewable age for Kerberos tickets depending on the authentication indicators attached to them.

You can define a unique Kerberos ticket policy that only applies to a single user. These per-user settings override the global ticket policy, for all authentication indicators.

Use the ipa krbtpolicy-mod username command, and specify at least one of the following arguments:

As an administrator, you can define Kerberos ticket policies for a user that differ per authentication indicator. For example, you can configure a policy to allow the IdM admin user to renew a ticket for two days if it was obtained with OTP authentication, and a week if it was obtained with smart card authentication.

These per-authentication indicator settings will override the user’s default ticket policy, the global default ticket policy, and any global authentication indicator ticket policy.

Use the ipa krbtpolicy-mod username command to set custom maximum lifetime and maximum renewable age values for a user’s Kerberos tickets depending on the authentication indicators attached to them.

Specify values for authentication indicators with the following arguments.