ClearPass: Custom Time Source Attributes

You can create custom date and time strings relative to "now" with the [Time Source] Authentication Source. This was useful recently when I needed to customise the expiration of MAC caching on Guest devices. 

Instead of having the MAC Caching last until the Guest Account expired, or a day or week from now I wanted the caching to last until midnight of the current day. Here is how I achieved it.

In the ClearPass Guest Authentication with MAC Caching template an attribute is written to the endpoint called "MAC-Auth Expiry". The value of the caching duration is derived in the MAC Caching Settings tab of the service template configuration wizard. By default it would be set to the Account Expiry Time using %{Authorization:[Guest User Repository]:ExpireTime} in the MAC Caching enforcement profile. to edit.

Note: I have used the prefix "deleteme" when using the Service Template so that I remember do remove the components it creates for this demonstration.

The value of Expire Time is extracted from the Guest User Repository so that it matches the Guest Account expiration when written to the Endpoint attribute.

%{Authorization:[Guest User Repository]:ExpireTime}

​The variable changes somewhat if you set the expiration to One Day or One Week however. Instead of pulling information from the Guest User Repository it instead uses the Time Source, which is a based on a SQL query.

%{Authorization:[Time Source]:One Week DT}

​"One Week DT" is just one of the options available by default as part of the default Time Source configuration.  It references the following SQL query which pulls the current time rounded to the hour and adds 1 week.

select date_trunc('hour', localtimestamp(0)+interval '1 week') as one_week

​There are various other examples built in to the time source such as Now DT, One Day DT, One Month DT and Six Months DT. These all display in a clear to read Date-Time format of YYYY-MM-DD HH:MM:SS. There are various other aliases that return an integer value relative to Epoch. I am less interested in calculating the time from a number so I will focus on the more readable form.

​To create a variable which would return my desired result I added an additional filter to the Time Source. This is found in the ClearPass Policy Manager under Configuration --> Authentication --> Sources. 

I called the Filter "Today at Midnight" and used the following Filter Query:

select date_trunc('day', localtimestamp(0)) + interval '23 hour 59 minutes 59 seconds' as tonight

​This query rounds the date-time to the current day and the time component is represented as 00:00:00. It then adds 23 hours, 59 minutes and 59 seconds resulting in data in the form of YYYY-MM-DD 23:59:59 (where YYYY-MM-DD is the current day). I then referenced tonight with the Alias Name of "Tonight DT" so I can use that in my Enforcement Profile variable.

​Save the filter and the Time Source. 
Now go to Enforcement --> Profiles and find your Guest MAC Caching profile for your service.
In the Attributes tab of the profile edit the Endpoint Attribute Value for the MAC-Auth Expiry so that it uses the new Time Source variable.

%{Authorization:[Time Source]:Tonight DT}

When a Guest successfully authenticates the Guest MAC Caching enforcement profile is called by the "User Authentication with MAC Caching Enforcement Policy". You will see it as one of the multitude of Actions taken.

The "MAC Authentication Role Mapping" policy (as created by the service template) is referenced by the "MAC Authentication Enforcement Policy". Notice in the first condition which defines the TIPS Role of {MAC Caching] checks the Endpoint MAC-Auth Expiry attribute and ensures that the present time is less than it.

​Now DT actually is rounded to the hour if you inspect the SQL query. I found this out when I was testing and had used an expiration of 5 minutes from now by using the following SQL query. Because of this, Now DT would not be granular enough if you needed expiration to occur in periods shorter than one hour and may require some further modification. There are possibly better ways to attack such a scenario however. Because "Now DT" will not be less than %{Endpoint:MAC-Auth-Expiry} at precisely midnight this works as expected.

SELECT date_trunc('second', localtimestamp(0)) + interval '5 minutes' as now_plus_5mins

The result of all of this is that upon subsequent MAC Authentication requests beyond the first date of connection the device is presented with a Captive Portal. In my use case this was a customised web-login page which required the username to be entered to resume the session. This would occur all the way until the Guest Account Expiration disables the account (which could be weeks, months or longer in to the future).

Let me know if this helps you out by commenting below or sharing in your social feeds.