A few years back I wrote a post about Accepting Raw Request Content with ASP.NET Web API. Unfortunately the process to get at raw request data is rather indirect, with no direct way to receive raw data into Controller action parameters and that hasn't really changed in ASP.NET Core's MVC/API implementation. The way the Conneg algorithm works in regards to generic data formats is roughly the same as it was with Web API.

The good news is that it's quite a bit easier to create custom formatters in ASP.NET Core that let you customize how to handle 'unknown' content types in your controllers.

Let's take a look.