Mocking external http calls for API testing in .NET Core

I want to write an API test, kind of end-to-end test, for my application.

Assume that I want to get all Foos in the system. When I hit an endpoint /foo/all, I fetch data using HTTPClient and get some dependent objects of Foo from another microservice Bar.

My unit tests are ok. I can also boot my api for tests , however I don't want to call Bar service as I don't want its dependency on my tests, instead, I want to make something like a stub.

So how can I mock those services? I cannot mock HttpClient and override ConfigureServices method in my test application bootstrap process, because HttpClient does not implement any interface.

Thanks.