Request.host returns `localhost` in Azure Functions using the worker model 'dotnet-isolated' and the ASP.NET Core integration

Question

I am trying to convert an Azure Function app from the worker model InProcess to Isolated Process. For this I have decided to use the aspnet-core-integration, so my HttpTrigger takes in Microsoft.AspNetCore.Http.HttpRequest req as an argument.

req.host is used to return a RedirectUrl for another function/endpoint running on the same domain, let's say https://foobar.com/public/server-configuration returns some json containing a RedirectUrl for https://foobar.com/public/authenticated-server-configuration.

Inside of the HttpTrigger for https://foobar.com/public/server-configuration I expected the req.host to be equal to foobar.com, but in this case I receive localhost, I get the feeling that it is somehow being rewritten locally.

This is just speculation but since my app is now being hosted in a different process, the host process for Azure functions will receive the request, startup a new process to handle the request, rewrite the request and sent it to the new process using localhost. Does anyone know what is going on? I was able to obtain the req.host using InProcess w/ the same infrastructure w.r.t proxies etc.

EDIT: maybe something like X-Forwarded-Host header would contain my real host?

Answer 1

Seems that X-Forwarded-Host is indeed a way to get the original req.host

I'm changing req.host to req.Headers["X-Forwarded-Host"] but maybe w/ some slight modifications for making it more robust.