The use of static credentials to establish a persistent database connection is against security best practices. 
Support for GCP IAM role-based auth has been added, AWS is more widely adopted than GCP. 
Extracting a DB connection string using AWS service account, as described by the AWS blog doesn't resolve the issue because such strings are invalidated every 15 minutes.
This is a library that seems promising for creating a IAM Role-Based connection for RDS. 
As a stakeholder in this initiative I'm actively working on an implementation. 
If a well tested solution that adheres to the coding standards of the project were made available as a PR, would it be possible to say that it could be included in the roadmap/upstreamed into the codebase within the next three to six months?