Estabeleça ligação ao Cloud SQL para Postgres com Go e autorizações da IAM

import (
	"context"
	"database/sql"
	"fmt"
	"log"
	"net"
	"os"

	"cloud.google.com/go/cloudsqlconn"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/stdlib"
)

func connectWithConnectorIAMAuthN() (*sql.DB, error) {
	mustGetenv := func(k string) string {
		v := os.Getenv(k)
		if v == "" {
			log.Fatalf("Warning: %s environment variable not set.", k)
		}
		return v
	}
	// Note: Saving credentials in environment variables is convenient, but not
	// secure - consider a more secure solution such as
	// Cloud Secret Manager (https://cloud.google.com/secret-manager) to help
	// keep secrets safe.
	var (
		dbUser                 = mustGetenv("DB_IAM_USER")              // e.g. 'service-account-name@project-id.iam'
		dbName                 = mustGetenv("DB_NAME")                  // e.g. 'my-database'
		instanceConnectionName = mustGetenv("INSTANCE_CONNECTION_NAME") // e.g. 'project:region:instance'
		usePrivate             = os.Getenv("PRIVATE_IP")
	)

	// WithLazyRefresh() Option is used to perform refresh
	// when needed, rather than on a scheduled interval.
	// This is recommended for serverless environments to
	// avoid background refreshes from throttling CPU.
	d, err := cloudsqlconn.NewDialer(
		context.Background(),
		cloudsqlconn.WithIAMAuthN(),
		cloudsqlconn.WithLazyRefresh(),
	)
	if err != nil {
		return nil, fmt.Errorf("cloudsqlconn.NewDialer: %w", err)
	}
	var opts []cloudsqlconn.DialOption
	if usePrivate != "" {
		opts = append(opts, cloudsqlconn.WithPrivateIP())
	}

	dsn := fmt.Sprintf("user=%s database=%s", dbUser, dbName)
	config, err := pgx.ParseConfig(dsn)
	if err != nil {
		return nil, err
	}

	config.DialFunc = func(ctx context.Context, network, instance string) (net.Conn, error) {
		return d.Dial(ctx, instanceConnectionName, opts...)
	}
	dbURI := stdlib.RegisterConnConfig(config)
	dbPool, err := sql.Open("pgx", dbURI)
	if err != nil {
		return nil, fmt.Errorf("sql.Open: %w", err)
	}
	return dbPool, nil
}