AWS Glue connection fails over SSL to RDS PostgreSQL database but works without SSL

Question

I have an AWS RDS PostgreSQL database setup that I would like to connect to using AWS glue using JDBC. My setup is simple, I have 1 VPC, 3 DB private subnets with a route for 0.0.0.0/0 that goes to NAT gateway, a security group that contains a self-referenced rule for all TCP ports inbound and an outbound rule that allows all traffic to 0.0.0.0/0.

Using the legacy glue connection tester, when SSL is disabled, the connection works so I know that

1. The JDBC URL is correct
2. The credentials are correct
3. VPC, Subnet, NACL, Security group configurations seems to be ok

However, when I enable SSL, the connection fails with the following message

Check that your connection definition references your JDBC database with correct URL syntax, username, and password. Check that your VPC/subnet has network access to AWS S3 and the connection definition contains a security group with an outbound port rule which can access S3

Inspired by this stackoverflow post and this aws lightsail article, I've tried downloading the AWS root certificates of various sorts including the ones bundled with intermediate certificates to an s3 bucket that I own and referencing that as the custom certificate in the glue connection SSL configurations.

I am aware that by default, AWS RDS databases are provisioned with an SSL cert for its connection endpoint, which would mean I should not need to upload a custom cert (if I understand this correctly), but I'm grasping at straws at this point.

Does anyone have any ideas on why the connection is failing over SSL?