login widget. present login/pass button

login.mflow.hs

-- normally to be used with autoRefresh and pageFlow when used with other widgets.
authenticateWidget ::  View Html IO ()
authenticateWidget=  wform $ do
   username <- getCurrentUser
   if username /= anonymous
         then do
           private; noCache;noStore
           return username   -- if it is logged alredy, return username to the first wcallback 
         else do             -- if not it tries to get the user/pass from the paramenters and log in if the user sent login/passw
          (name, pass) <- (,) <$> (getString Nothing <! hint "login name"
                                    <! size' (9 :: Int)
                                    <++ br)
                              <*> (getPassword <! hint "password"
                                    <! size' 9)
                              <++ br
                              <** submitButton "login"
          val  <- userValidate (name,pass)
          case val of
            Just msg -> notValid msg
            Nothing  -> login name >> clearEnv >> (return name)
   -- if one of the two return the user, then wcallback erase the login/password boxes and present  logged as .... logout
   `wcallback` (\name -> ftag "b" (fromStr $ "logged as " ++ name++ " ")
                     ++> pageFlow "logout" (submitButton "logout")) -- wlink ("logout" :: String) (ftag "b" $ fromStr " logout"))
   
   -- the second callback is activated when  logout is pressed, and call wlogin to present the login/pass boxes again
   `wcallback`  const (logout >> clearEnv >> authenticateWidget)

focus = [("onload","this.focus()")]
hint s= [("placeholder",s)]
size' n= [("size",show n)]