How can I test OAuth before making it public?

Hi, I want to implement OAuth for my app but as I can understand from the docs, I can do it only after making it public.

Until then I receive: `This app is private and can’t be installed or authorized `

So, I tried to make my app public but intercom crew sent me this: "We need to see OAuth in action to make sure it's working"

Please help, I'm a bit stuck.

Thanks in advance