Token is generated at the endpoint but does not arrive on the page

I want to create a website with Svelte/Kit and use JWT.I have found instructions on the internet, for example:Svelte JWT Authentication https://morioh.com/p/1d95522418b2SvelteKit Session Authentication Using Cookies https://www.youtube.com/watch?v=bG7cxwBMVagBut unfortunately no instructions for Svelte Kit and JWT. So I tried it myself.

The token is generated at the endpoint, but does not arrive on the page (or is not callable). I suspect that some setting in the headers is wrong, but can't figure out what is wrong. This is my highly simplified test environment:

(1) I call the endpoint login.js from the page index.svelte. For testing, I omit checking email and password and send JWT right back. Data arrives, but I don't see the JWT.

(2) The JWT should be sent to another endpoint. What is the best way to do this?

The "page" index.svelte (simplified):

<script>  let email="", password="";  const doLogin = async () => {    const response = await fetch("/auth/login", {      method: 'POST',      headers: {"Content-Type": "application/json",      },      credentials: 'include',      body: JSON.stringify({    email,    password      })    });     if (response.status == 200) {      const { done, value } =         await response.body.getReader().read();      await console.log("done, value=", done,         JSON.parse(new TextDecoder("utf-8").decode(value)));      await console.log("headers=", response.headers);    }  }</script><h1>Welcome to MyAuth</h1><input type=email bind:value={email}/><br/><input type=password bind:value={password}/><br/><button on:click={doLogin}>Submit</button>

The "endpoint" login.js (simplified):

import jwt from "jsonwebtoken";  export function post(request, context) {  const token = jwt.sign({    data: { text: "test" },"topsecret",   });    const response = {    status: 200,    headers: {'content-type': 'application/json','Authorization': `Bearer ${token}`,    },    body: {      passwordOk: true,    }  };  return response;}

The console shows:

done, value= false {passwordOk: true}index.svelte:59 headers= Headers {}index.svelte:44 Fetch finished loading: POST "http://localhost:3000/auth/login".doLogin @ index.svelte:44