If you're interested in setting up OAuth in FileMaker 16, Google is a good option to get started with. I've posted a detailed step-by-step tutorial that will guide you through the process. The FileMaker part of the problem is pretty straightforward but the Google part isn't. The tutorial will get you through it (at least until Google changes its API website).
The pdf can be found here:
Hope this is helpful to someone. I'm finishing a similar tutorial on OAuth through Microsoft but won't have time to polish and revise until next week.