Access to fetch.. has been blocked by CORS policy: Response to preflight request doesn't pass access

Shopify Apps
1

I’m trying to generate an access token for my public app. However, I’m getting this error,

Access to fetch at 'https://test.myshopify.com/admin/oauth/access_token' from origin 'https://mydomain.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I already tried adding the “Access-Control-Allow-Origin” on the request header, but I’m still getting that same error.

export function* postShopify(postData, access_token_url, content_type) {
    return yield fetch(`${access_token_url}`, {
        headers: {
            'Access-Control-Allow-Origin': '*',
            'Content-Type': `${content_type}`,
        },
        method: 'POST',
        postData,
    });
}

Is there a workaround solution you could recommend to fix that error without using the App Proxy?

Here are the references I used on how I can generate the access token

  1. https://shopify.dev/docs/apps/build/authentication-authorization/access-tokens/#authorization-code-grant
  2. https://www.shopify.com/ph/partners/blog/17056443-how-to-generate-a-shopify-api-token