Set header from server middleware

export default defineEventHandler(async (event) => {
    const token = await $fetch('https://xxx.kinde.com/oauth2/token', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/x-www-form-urlencoded',
        },
        body: new URLSearchParams({
            audience: "https://xxx.kinde.com/api",
            grant_type: "client_credentials",
            client_id: "xxx",
            client_secret: "xxx",
        })
    }) as { access_token: string };

    // I have tried
    event.headers.set('authorization', token.access_token);
    // I have tried
    event.node.req.headers.authorization = token.access_token;
})

  const properties = await $fetch(`https://xxx.kinde.com/api/v1/users/${event.context.params?.user}/properties`, {
    method: 'GET',
    headers: {
      'Accept': 'application/json',
    }
  });