I'm trying to connect to get a secret from google's secrets manager, and the same code works for Cloud Functions, but not for App Engine.

const { SecretManagerServiceClient } = require('@google-cloud/secret-manager');

const secretManagerServiceClient = new SecretManagerServiceClient();
const name = 'projects/000000000000/secrets/database/versions/latest';

exports.testSecretManager = async (req, res) => {
  const [version] = await secretManagerServiceClient.accessSecretVersion({ name });
  const payload = version.payload.data.toString();
  console.debug(`Payload: ${payload}`);
  res.sendStatus(200);
};

The same code works fine when I deploy it as a function.

But when I run the same code as a part of App Engine application. It fails with this error:

Error: 16 UNAUTHENTICATED: Failed to retrieve auth metadata with error: Could not refresh access token: Unsuccessful response status code. Request failed with status code 500
    at Object.callErrorFromStatus (/workspace/node_modules/@grpc/grpc-js/build/src/call.js:31:26)
    at Object.onReceiveStatus (/workspace/node_modules/@grpc/grpc-js/build/src/client.js:180:52)
    at Object.onReceiveStatus (/workspace/node_modules/@grpc/grpc-js/build/src/client-interceptors.js:365:141)
    at Object.onReceiveStatus (/workspace/node_modules/@grpc/grpc-js/build/src/client-interceptors.js:328:181)
    at /workspace/node_modules/@grpc/grpc-js/build/src/call-stream.js:182:78
    at processTicksAndRejections (node:internal/process/task_queues:78:11)

I believe both Cloud Functions and App Engine are managed by the same service account “App Engine default service account”. And it has rights.

It seems like GOOGLE_APPLICATION_CREDENTIALS is missing from the environment.

console.log(process.env.GOOGLE_APPLICATION_CREDENTIALS); gives me undefined. Can this be a reason? How do I pass this environment to app engine then?

How can I deeper debug this?