Best Approach for Making Web API calls from MVC app (with option of adding third-party apps)?

I'm looking for some architectural advice and have spent hours researching without clear direction.

I want to create an ASP.Net MVC 5 app which makes periodic calls to a Web API 2 service (both on the same domain).

Users will sign up via the MVC app (create username/password), then the MVC app will automatically poll the Web API service at regular intervals, without further intervention (polling is indefinite, and user should not have to login again or provide additional input).

In the future, I would like other developers to integrate custom apps with the Web API service, also polling at regular intervals.

It seems like OAuth2.0 is the way to go, but I haven't found a clear example in this particular scenario.

Any suggestions?