Registered bank slip is a payment method that contains sensitive data of the customer who is making the purchase.
When a customer informs their data to close an order, the information for First Name, Last Name, CPF etc. is used for generating the registered bank slip.
This information is saved in the customer profile and is displayed in the registered bank slip. In this way, authentication works as a security measure so that fraudsters can not access the information.
Because of this, the login is requested both at the time of choosing the registered bank slip as payment method and the time of getting the bank slip in the page of Order Placed.
Authentication is required only as of the second purchase. Since during the first purchase the data is being saved for the first time, there's no need for authentication. The registered bank slip will be issued with the data informed in this first purchase and only the person who filled the information will have access to them.