These pages are authorization page of an Access Control Server (ACS) in the 3-D Secure flow. Visa/MasterCard designed the scheme, but the spec is open (in a som

These pages are authorization page of an Access Control Server (ACS) in the 3-D Secure flow. Visa/MasterCard designed the scheme, but the spec is open (in a somewhat limited sense), so anyone can implement the ACS as long as you're qualified to see the spec and can get it certified. Banks are free to choose the ACS vendor as long as it's certified. Many banks do provide ACS authorization page at their own domain name, although a many of them just use a third party service just like in your case.