fix: throw error when Auto IAM AuthN is unsupported (#310)

Fixes #283.

dialer_test.go

@@ -249,6 +249,58 @@ func TestIAMAuthn(t *testing.T) {
 	}
 }
 
+func TestIAMAuthNErrors(t *testing.T) {
+	tcs := []struct {
+		desc    string
+		version string
+		opts    Option
+	}{
+		{
+			desc:    "when the database engine is MySQL",
+			version: "MYSQL",
+			opts:    WithIAMAuthN(),
+		},
+		{
+			desc:    "when the database engine is SQL Server",
+			version: "SQLSERVER",
+			opts:    WithIAMAuthN(),
+		},
+	}
+
+	for _, tc := range tcs {
+		t.Run(tc.desc, func(t *testing.T) {
+			inst := mock.NewFakeCSQLInstance("proj", "region", "inst",
+				mock.WithEngineVersion(tc.version),
+			)
+			svc, cleanup, err := mock.NewSQLAdminService(
+				context.Background(),
+				mock.InstanceGetSuccess(inst, 1),
+				mock.CreateEphemeralSuccess(inst, 1),
+			)
+			if err != nil {
+				t.Fatalf("mock.NewSQLAdminService(): %v", err)
+			}
+			defer cleanup()
+
+			stop := mock.StartServerProxy(t, inst)
+			defer stop()
+
+			d, err := NewDialer(context.Background(),
+				WithTokenSource(mock.EmptyTokenSource{}), tc.opts)
+			if err != nil {
+				t.Fatalf("NewDialer failed with error = %v", err)
+			}
+			d.sqladmin = svc
+
+			_, err = d.Dial(context.Background(), "proj:region:inst")
+			t.Log(err)
+			if err == nil {
+				t.Fatalf("version = %v, want error, got nil", tc.version)
+			}
+		})
+	}
+}
+
 func TestDialerWithCustomDialFunc(t *testing.T) {
 	inst := mock.NewFakeCSQLInstance("my-project", "my-region", "my-instance")
 	svc, cleanup, err := mock.NewSQLAdminService(

internal/cloudsql/refresh.go

@@ -21,6 +21,7 @@ import (
 	"crypto/x509"
 	"encoding/pem"
 	"fmt"
+	"strings"
 	"time"
 
 	"cloud.google.com/go/cloudsqlconn/errtype"
@@ -357,6 +358,12 @@ func (r refresher) performRefresh(ctx context.Context, cn connName, k *rsa.Priva
 	case <-ctx.Done():
 		return md, nil, time.Time{}, fmt.Errorf("refresh failed: %w", ctx.Err())
 	}
+	if iamAuthN {
+		if vErr := supportsAutoIAMAuthN(md.version); vErr != nil {
+			return metadata{}, nil, time.Time{}, vErr
+		}
+	}
+
 	var ec tls.Certificate
 	select {
 	case r := <-ecC:
@@ -375,3 +382,14 @@ func (r refresher) performRefresh(ctx context.Context, cn connName, k *rsa.Priva
 	}
 	return md, c, expiry, nil
 }
+
+// supportsAutoIAMAuthN checks that the engine support automatic IAM authn. If
+// auto IAM authn was not request, this is a no-op.
+func supportsAutoIAMAuthN(version string) error {
+	switch {
+	case strings.HasPrefix(version, "POSTGRES"):
+		return nil
+	default:
+		return fmt.Errorf("%s does not support Auto IAM DB Authentication", version)
+	}
+}