How to use variables instead of plain secrets in data.metadataConnection airflow helm chart

How to use (env) variables instead of plain secrets in data.metadataConnection in values.yaml

VAR_USER = "username"
VAR_PASS = "password"

data:
  metadataConnection:
    user: VAR_USER
    pass: VAR_PASS
    protocol: postgresql
    host: ~
    port: 5432
    db: VAR_DB
    sslmode: disable

instead of

data:
  metadataConnection:
    user: postgres
    pass: postgres
    protocol: postgresql
    host: ~
    port: 5432
    db: postgres
    sslmode: disable