Salesforce - count actual users of a commercial add-on (APEX) SFDC application

How can a commercial SFDC application that is sold on the basis of the number of users (for that application) a开发者_开发技巧ctually govern proper usage once it is deployed by an organization on their SFDC.

For example, say that there is a quoting application on AppXchnage. A certain company has purchased 20 licenses but they have a total of 50 users in their SFDC organization.

The purpose would be to allow "static" deployment of up to 20 selected users.

Is it at all possible, and if so how?

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Well, you can always either keep track and count actual users in a custom object or have a form to assign user licenses to that object before use. Either way, however, i can only use security through obscurity and a skilled admin with dev background can bypass it one way or another. As you know most per-user-license apps have a external component which handles licensing among other things.

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Salesforce has this for you. Once you've created your application you can register it with an License Management Application (LMA). It helps you track installation and upgrades of your application and lets you apply licensing so you can control how many users in the customers org can access your package and for how long.

For more info check out the LMA Documentation. You can also watch this presentation that gives an overview of LMA.