Problems exchanging customer API access token on hydrogen storefront

Shopify Discussion
1

I am using the createCustomerAccountClient function from Shopify’s hydrogen package to manage authentication on my headless storefront. The problem is that the refresh token cannot be exchanged from shopify’s server. I am using a local version of Hydrogen to debug (with no changes) and am receiving an unsupported_grant_type error.

The access grant included - its type or another attribute - is not supported by the authorization server.

This error clears the session and the user is shown as no longer logged in every hour. I can’t seem to find any documentation on the proper grant type to use or why this is failing. This is the code from the hydrogen package:

  const body = new URLSearchParams();

  body.append('grant_type', 'urn:ietf:params:oauth:grant-type:token-exchange');
  body.append('client_id', clientId);
  body.append('audience', CUSTOMER_API_CLIENT_ID);
  body.append('subject_token', authAccessToken);
  body.append(
    'subject_token_type',
    'urn:ietf:params:oauth:token-type:access_token',
  );
  body.append('scopes', 'https://api.customers.com/auth/customer.graphql');

  const headers = {
    'content-type': 'application/x-www-form-urlencoded',
    'User-Agent': USER_AGENT,
    Origin: httpsOrigin,
  };
  const startTime = Date.now();
  const url = customerAccountTokenExchangeUrl;
  const response = await fetch(url, {
    method: 'POST',
    headers,
    body,
  });