Small piece of asp.net core routing code

Hello, I have a small need for a piece of ASP.NET Core routing code. I want to route as the default, but I want to also route based on the subdomain. I would think that this is pretty straightforward, but I've just been fumbling around with documentation. Note that this is ASP.NET Core! I think that I just need a custom router class (with what references I need), and how to add the route. I would think that the subdomain could be passed in as an additional parameter in my controller methods. The deliverable would be the code file or files that I can drop into my project and run. Include in your bid how long, in hours, you expect this to take.