Licencing PHP application

I have written a PHP application for a company I work for, now they want to licence it out to other companies to use.  Part of this application allows the administrator to add other user and devices that are monitored.
What we would like to do is be able to limit the number of users/devices that can be added according to which licence our customers buy.
One way I thought of doing this is to have the application Zend encoded, and within a PHP file a variable that will relate to the number of users that are allowed to be added.
id like to hear from anyone who has done anything like this before, and if there is a good secure way to go about this.
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Is this an internet or an intranet application? Otherwise you could always implement a mysqltable on your databaseserver and have each system connect to that system when a user gets added. This mysql user would only granted read access on the one particular table offcourse.

You then could zendencode the project to prevent changing of the mysql retrieval.


Encoding your project with Zend and also encoding the lincence-file with the settings will prevent the client from changeing those setted values or even getting to know which variables must be changed.
Or you might encode all those settings into the licencekey which then could be plaintext on the client side.

Using a central point to verify add/user and so on will typical not possible in any larger firm and that might be KO-cirteria to use your product. Endoce it with Zend and you are on a good, secure side. I would never buy such a product as it may not work if you need to change that position of the server my application may not be function anymore.

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maundedAuthor Commented:
Thanks folks!
I wrote a short licence.php file which has a couple of functions that check the number of users in teh db and compare them to a variable in that file.  Used Zend Encoder to make it a bit trickier to break :)
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