fix: require TLSv1.3 when connecting using IAM authentication

[shubha-rajan]

Change Description

Require TLS v1.3 when connecting with IAM auth so that OAuth2 token is encrypted during handshake.

Checklist

• Make sure to open an issue as a
  bug/issue
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea.
• Ensure the tests and linter pass
• Appropriate documentation is updated (if necessary)

Relevant issues:

• Fixes b/183540928 (internal)

[dooman87]

Hi there,

Am I thinking right that without the support of TLS1.3 the IAM auth into Postgres won't work? Looks like AppEngine Standard Java 8 environment doesn't support TLS1.3 and I was thinking if there are any workarounds?

[kurtisvg]

@dooman87 Unfortunately, IAM DB AuthN requires TLS 1.3 and there aren't any workarounds. Are you sure that GAE-Standard doesn't support TLS 1.3?