Amazon Sign-in allows users to login to your shop using their Amazon username and password. The name, email address and user id is fetched from Amazon in order to facilitate the creation of a Magento account. Shipping and billing address will be retrieved as part of the checkout.
Customers who have logged in via Amazon Sign-in previously, will be recognized and automatically logged in into the Magento customer account as well. In case an account for the email address already exists, the accounts can be linked to add Amazon Sign-in as another option to sign in for the customer.
When enabled, Amazon Sign-in will log customers into Magento via their Amazon
If disabled, customers using Amazon Pay will be handled as Guests by default but prompted to optionally create an account during Checkout.
if Amazon Sign-in is disabled and Magento Guest Checkout is disabled, the customer will be able to see and use Amazon Pay buttons only if already signed in with a Magento account.