Is your feature request related to a problem? Please describe.
Currently, there is a restriction for the database username which will limit the certificate-based authentication. It's very common to include .local (e.g.:  internal-service2.local) in the CN (Common Name) of a certificate.  The AWS Certificate Manager (ACM) won't even issue a certificate if the "dot" (.) is not present.

Describe the solution you'd like
Could you please include dot (.) and hyphen (-) in the whitelist for the database username ?

Thank you,

Vinod