How to force the customer to register first

I want to force the customer to register first then be able to add the item to the cart. Even though I've set the "Purchase Document" for "Registered" under the configuration but it is still redirecting to the cart page if I click the login button without entering any info. And system takes the customer to complete the purchase process without registering.Please see the attached images for more details.

I don't want the customer enter into the purchase process without registration.

I'll really appreciate your help as I need to install the component on the client site asap.

Thanks