Could you explain a little more what this app would do? Do you want to allow players to play games on OGS/interact with OGS in some other way? This is possible, and there are quite a few forum posts about it. For example, OGS API notes
Or are you just looking for SSO? In other words, a way to link the OGS account and log in with the same credentials, but the user does not interact with OGS besides authorization. I don’t believe OGS supports this, but I would find such a feature useful!