Handling conditional requests in ASP.NET Core MVC

This is another post resulting from my work on sample ASP.NET Core MVC powered Web API. This time I'm going to focus on conditional requests. Conditional requests have three main use cases: cache revalidation, concurrency control and range requests. Range requests are primarily used for media like video or audio and I'm not going to write about them here (I did in the past in context of ASP.NET MVC), but the other two are very useful for a Web API.