The inability to access TNEW Test via our own domain name and its impact on shared sessions has been a continual source of frustration during web development. It's one more variable we need to account for when troubleshooting our API integrations, and when we inevitably mess up the timing our cross-domain cookie support requests, development grinds to a halt for hours. Please return support for ANAME records, as you had prior to the AWS migration.
As a stopgap measure, please allow cross-domain cookie support to be enabled indefinitely on Test. The current seven day expiration invariably hits in the middle of some time-sensitive testing of our TNEW integration.