AWS IoT is announcing a new feature for AWS IoT Core called “Multi-Account Registration,” which is now available in beta. The new feature allows customers to quickly move devices between their AWS accounts by specifying the account information when the device connects to AWS IoT Core. Customers opting to use this feature will use Server Name Indication (SNI) strings sent by a device and as part of the Transport Layer Security (TLS) session to route to the correct AWS IoT endpoint.

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/09/aws-iot-core-introduces-beta-feature-to-simplify-device-certificate-registration/