PayPal introduced a universal sign-in button of its own, for online merchants. Similar in function to "Sign-in with Facebook" button, the "Log-in with PayPal" button signs you in with a participating online merchant, and instantly gives them your shipping and billing information each time you check-out, while concealing your credit card or bank account information. With certain merchants, it even handles buyer protection.
Unlike Facebook's button, which is practically instant if you've set the site to remember your credentials, PayPal button requires you to log-in with your PayPal e-mail address or phone-number; and password or PIN. At least you're saved of a lengthy registration form that follows. You can log-in with PayPal after you've filled up your shopping-cart, so the merchant doesn't get any of your details, if you don't like anything. PayPal will pilot the button with a select few merchants, its biggest pal eBay could feature in that list.