Generate a complete URL within a Yesod application

I mean that for example

YC.getUrlRender >>= enact where
    enact renderURL = renderURL HomeR

will result in "/", for example, and usually that's what you need. However, I'm trying to crack email verification where the email has to contain the http://ift.tt/1HM6vhv bit as well so that the user can click on the link to verify the new account. Is it in fact possible to obtain that bit ? In my deployment for example, the Yesod application is behind nginx, with the configuration:

location / {
    proxy_pass http://127.0.0.1:3000;
}

so would the Yesod app even know that it was reached via http://ift.tt/1bv1Qmc ?