Site.hs

loginRequired = requireUser auth handleRedirect
  where
    -- this is the cleanest way (afaik) to write it
    handleRedirect = withRequest (redirect . append "/login?to=" . rqURI)
    
-- that handleRedirect can be rewritten in a more imperative way:
handleRedirect = withRequest (\rq -> redirect (append "login?to=" (rqURI rq)))

-- or
handleRedirect = withRequest (\rq -> redirect . append "login?to=" . rqURI $ rq)

-- or?
handleRedirect = withRequest
  (\rq ->
     let uri = rqURI rq
         loginRoute = append "login?to=" uri
     in redirect loginRoute)