Checkout should log user in instead of simply taking the username and password
When ordering a new service the checkout has the option to create a new account or use an existing one.
However when using an existing one if doesn't actually log you in and instead just takes the username and password.
The biggest problem is this makes it impossible for a user to use an existing credit card. It's also very confusing and odd from a user perspective.
Instead when checking out and using an existing account a user should be logged in and allowed to select an existing credit card.
This seems so basic that it shouldn't even need to be a feature request.