How to use the website URL as base URL for Axios requests in a Nuxt.js app - axios

Question

I have a webapp deployed and it's visitable via the domain url www.myapp.com.
Also I have a backend deployed that is called by a middleware calls via nuxt.config.js and serverMiddleware.
serverMiddleware: [
{ path: '/backend', handler: '~/api/backend.js' }
]
When deployed and using Axios out of the box the calls to the backend/middleware are done by http://localhost:3000 instead of www.myapp.com. Therefore CORS is being triggered and giving me this error in the console:
Access to XMLHttpRequest at 'http://localhost:3000/backend/packingplan/all?owner=123' from origin 'https://www.myapp.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.
So I did a little research and found out that I can override the base URL Axios uses. That way I can turn the http://localhost:3000 into www.myapp.com and avoid the CORS problem.
I am doing this like this:
create a Nuxt plugin ~/plugins/axios.js
add the following code
export default function (context) {
context.$axios.defaults.timeout = 15000
context.$axios.defaults.baseURL = context.$config.baseUrl || 'http://axios.plugin.failed'
}
add the plugin to the nuxt.config.js
plugins: [
'~/plugins/axios.js'
]
And this works. Now the CORS problem is solved.
BUT
It just works when I call my app with www.myapp.com. As soon as I open my webapp without the www then CORS is triggered again.
Access to XMLHttpRequest at 'https://www.myapp.com/backend/packingplan/all?owner=62443cb7d0f6b2006a8526e5' from origin 'https://myapp.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.
So I wonder if I can tell Axios somehow to use the URL that is defined in the browser? If the user is visiting the site via www.myapp.com it should use that as Base URL for Axios and if the user is visiting the site via myapp.com it should use that one?
How can I achieve that? Any ideas?