Google Cloud Functions ACP local testing WON'T WORK!

[finnDiesel234xX]

I have a NextJS / Typescript webapp. The backend of the webapp is supposed to call my Google Cloud Function, called "python-http-function" under project name "python-serverless-test-1". This is not a public function. I am testing my webapp locally, meaning with "npm run dev" and testing out calling my cloud function.

I am using ADC (Application Default Credentials), which finds the credentials in whatever current environment is being run. For local/development in this case, I provided user credentials to ADC by running the "gcloud auth application-default login" command, which created a file in $HOME/.config/gcloud/application_default_credentials.json. This file exists, I verified.

When I actually execute the call to python-http-function with the following code, however, it errors:

// source for this code: https://cloud.google.com/functions/docs/securing/authenticating#generating_tokens_programmatically
  
const targetAudience = 'https://us-west1-python-serverless-test-1.cloudfunctions.net/python-http-function'
  const url = targetAudience;
  const auth = new GoogleAuth();
  const client = await auth.getIdTokenClient(targetAudience);

  // Create a FormData object to hold the form data.
  const formData = new FormData();

  // Add the form data to the FormData object.
  formData.append('pdf', 'data');

  // Make the request to the Cloud function.

  const res = await client.request({
    url: url,
    method: 'POST',
    body: formData,
  });

Error:
error Error: Cannot fetch ID token in this environment, use GCE or set the GOOGLE_APPLICATION_CREDENTIALS environment variable to a service account credentials JSON file.

 I verified that gcloud can find the JSON credentials file by running gcloud auth application-default print-access-token and seeing it print it out. What is going on here? What am I missing? 

Thanks!