Is it possible to customize login page so that we can work without login as well.

For e.g. if we launch Amazon.in, Login is not mandatory. Without login also i can order any product from there website.

My requirement is similar to that only. In home page i want to display list of products and option to login in top right corner.

For some of the products customer should be able to proceed with there orders without login.

For some of the products customer must have to login first then only they can proceed with there orders. 

So if the customer logins his/her details will be auto populated (like name, address, etc), if not i need to ask each and every field from customer. But customer should able to proceed in both the cases - with or without login for free products. 

Here i am not talking about SSO (or any other authentication methods), as customer will be outside my organization. This portal will be used by customers. Any new customer can explore my portal and if likes uses the same for placing any orders.