Need API and special file handler for appsettings.json

I'm trying to write a connection string for .NET Core Web Application with an Empty template in order to add Azure Storage, but the file that it needs to be written to (appsettings.json) doesn't exist. It looks like based on discussion off [this related issue](https://github.com/dotnet/project-system/issues/2402), I need an API that will create such a file if it does not exist, and return some kind of a handle to it.

Please let me know if you need more information.