EDIT: see conclusion at the end of this post.
First off, let me clarify I've found a few similar questions/answers on SO, but none that apply to my particular situation. The one that came closest is this one but it doesn't address the AirWatch aspect.
So I'll try to be very specific.
Background
I have an iOS application that's free. I also have the same app for Android and Windows 10 but those are not my concern. The iOS app is available to anyone from the App store. But I have a few large corporate customers who use AirWatch to manage the installation/update cycle of their devices. They either have Enterprise or VPP Apple accounts. They want me to provide them with the IPA file so they can distribute it themselves through AirWatch. In my mind, that's a perfectly legitimate request: they just want to have better control over what gets installed on their devices.
Problem
From what I understand, an Enterprise account requires that the application be signed with the customer's certificate. But if I have several such customers, that means I have to re-sign each application for each customer, every time I have a new update available. And those customers that have VPP accounts cannot use them because the VPP program only applies to paid apps, not to free ones.
Note: keep in mind that at that stage when I'm ready to provide the app to these customers, the app has already been reviewed and accepted by the App Store. So it's deemed legit.
After googling this matter for a while, I know it's possible for someone else to resign an app or to sign it for the first time if it is provided in unsigned form to start with. However, resigned apps are apparently not supported by AirWatch (and, I assume, other MDM's as well).
If that information is incorrect, then I guess all I would need to know is the recipe that I, as a coder, have to follow before providing the app to my customers and what kind of steps they have to take in order to deploy using AirWatch.
Question
So how do I get my free app to my customers so they can manage the distribution themselves, without me having to go through yet another set of hassles every time I change something. Remember: if I only had a single corporate customer I wouldn't give it a second thought and I would just use their own certificates but I have several potential customers with the same requirements, so the point is to make it easy for all of them and for myself.
I hope my question was clear enough, thanks in advance for any help.
EDIT - Conclusion: I was able to validate that an unsigned IPA file can be signed with the customer's certificate and uploaded to their AirWatch distribution app. Which means I simply have to provide the unsigned version to any customer with the same issue and they will be able to distribute the app themselves with their MDM. Hope this information helps others.