Let I have made a small program for MS Windows (using C++). And I want to sell it via subscription.
Does Patreon API allows it?
How?
You would likely need a central place to redirect oAuth logins - ie after the user authorizes your app at Patreon, s/he would need to be directed somewhere which will receive the codes sent by API and start a session through some mechanism.
If you have a central server which handles oAuth logins, then your users can create accounts in that central server (through order process etc), and then unlock your plugin by logging into that system via Patreon.
For remote windows software installs, some kind of license thing to identify a remote install and connect to your server to check its validity will likely be necessary. This may be made mandatory to run the software, or alternatively required to receive updates. Or both.