Depending on your individual network setup, the original host might also be availale in a header.

In that case, you might find the URL, you are looking e.g. in:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Origin

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-Host

You can access these as follows.

Request.Headers["X-Forwarded-Host"];