Store the ApiUrl in the message, so that user can't change it midway.

src/Scylla/Http.elm

@@ -67,7 +67,7 @@ login apiUrl username password = request
             ] )
         , ("password", string password)
         ]
-    , expect = expectJson ReceiveLoginResponse loginResponseDecoder
+    , expect = expectJson (ReceiveLoginResponse apiUrl) loginResponseDecoder
     , timeout = Nothing
     , tracker = Nothing
     }

src/Scylla/Model.elm

@@ -41,7 +41,7 @@ type Msg =
     | ViewportChangeComplete (Result Browser.Dom.Error ()) -- We're done changing the viewport.
     | ReceiveFirstSyncResponse (Result Http.Error SyncResponse) -- HTTP, Sync has finished
     | ReceiveSyncResponse (Result Http.Error SyncResponse) -- HTTP, Sync has finished
-    | ReceiveLoginResponse (Result Http.Error LoginResponse) -- HTTP, Login has finished
+    | ReceiveLoginResponse ApiUrl (Result Http.Error LoginResponse) -- HTTP, Login has finished
     | ReceiveUserData Username (Result Http.Error UserData)
     | ReceiveCompletedReadMarker (Result Http.Error ())