Aug 17, 2016 05:12 AM|Yohann Lu|LINK
You can make a secured API call using the application credentials means that the user has already authenticated and the request has her bearer token. Given that WebApi has authorized the user, there may be a built in way to access the userId.
In WebApi 2 you can use RequestContext.Principal to get user messages from within a method on ApiController.
Secure a Web API with Individual Accounts and Local Login in ASP.NET Web API 2.2: