Ask HN: Did you develop an in-house license server or buy it?

I'm working on a couple of projects that require a licensing system; think of engineering software like Solidworks.

How does everyone else do this? I'm basically interested in a vote of whether most people roll their own, or if there's a popular off-the-shelf choice to simplify the task.

My requirements are:

* Should be manageable through a web interface (activate, de-activate, etc)

* Ideally, the software would be able to tolerate a lack of network connectivity for some amount of time

* Should allow us to charge using either a single payment model, or a subscription model

* Should be easy to integrate with a C++ application