Interesting, building a YubiKey-based domain controller is on my list of things to do as we slowly work my way up the value chain and go after bigger projects - all on-prem and offline. The problem is we're years away from needing it, and even in the best case scenario our sales pipeline is 3-5 years.

Almost all of our software is in-house as we're very adept and efficient coders and it keeps the dependencies to a minimum, especially with regards to the licensing. We only have a single non-royalty free dependency and it's a total nightmare, the component is probably responsible for 30% of revenue but 95% of headaches.

So I'm trying to think of a hypothetical where we would buy such a product. Basically if I could have the same flexibility of making such software ourselves I would pay up to what we could expect it would cost to make it. If we were to need it it would be for a ~$1-3M USD project which we could carve off ~$100K for something like this due to the expected dev time savings which could be redirected to other areas while we scale up for the project. But for the second time round pony up bigger chunk say ~$200K to cover the cost of building it ourselves.

We were looking on standardizing on YubiKey, probably for the same reasons you went with them. Honestly I don't think my company should be your target market, we make software and are very good at it so it's a bit hard to sell us software, but if you decide to give out your contact details I'll make a note of it and keep an eye on what you choose to do.