Sounds like ngrok SDKs (https://ngrok.com/categories/sdks), but its closed source so I guess falls foul of your 3rd party solution comment.

Another option could be zrok (https://zrok.io/), which is an alternative that is open source, and also includes SDKs - https://blog.openziti.io/the-zrok-sdk.

I work on its parent project, OpenZiti, which also may fit your idea. Either way, its a programmatic way to embed connectivity into your app, making it accessible anywhere, but only to people who have authenticated and authorised, its others invisible.