@John Fak Thank you for reaching out.
Yes, this is correct. Azure Cache for Redis supports only AAD artifacts as users currently. We do not have support for only username/password combination on the roadmap right now, but your feedback has been duely noted.
We recommend you also to raise this feedback over Azure Feedback Channel for Azure Database for Redis Cacheso that concerned team could consider this feature depending on the importance and up-votes received.
Hope that answered your question.
Regards,
Oury