Здоровенькі були, Igor!
I'd recommend you to review Kentico documentation on custom authentication topic:
https://docs.kentico.com/display/K81/Handling+custom+external+authentication
https://docs.kentico.com/display/K81/Handling+custom+claims-based+authentication
It looks like you're trying to implement you authentication page, but Kentico recommends you to use their form, but handle SecurityEvents.Authenticate.Execute
event where you can verify user creds against third party system and fetch some user data if it is valid.
Hope this helps a bit.