I can do local auth with the below code using my service account credentials. Set in .env as GOOGLE_APPLICATION_CREDENTIALS=./service-account-key.json

try {
 const auth = new google.auth.GoogleAuth({
 scopes: SCOPES,
 clientOptions: {
 subject: "user@email.com",
 },
 });
 const gmail = google.gmail({ version: "v1", auth });
 return gmail;
 } catch (e) {
 console.error(e);
 return null;
 }

But I'm trying to figure out how to get this working on Cloud Run using the service account on there.. I assumed the auth stuff would be passed in automatically, which doesn't seem right, but also couldn't find any documentation to show otherwise. Has anyone done this before? Any alternatives I can try here?