How to add a user's public IP to the X-Forwarded-For header using SvelteKit and TypeScript?

I'm developing a web application with SvelteKit and TypeScript. During the login process, I aim to send the logged-in user's public IP information in the headers.

event.locals.clientIP = event.getClientAddress();

event.getClientAddress() just return local ip.

How can I correctly add the logged-in user's public IP to the X-Forwarded-For header?

Additional Info:

I'd prefer not to use external APIs to fetch the public IP due to potential security vulnerabilities. Is there an alternative method to obtain the IP?

It's possible to get the client IP on server side:

+page.server.ts:

/** @type {import('@sveltejs/kit').RequestHandler} */
export async function load(event) {
    return { ip: event.getClientAddress() };
}

And access it on client side:

+page.svelte:

<script lang="ts">
    import type { PageData } from './$types';
    export let data: PageData;
</script>

{#if data?.ip}
    <p>ip to test: {data.ip}</p>
{/if}

Note that when running on localhost, you'll get your local IP, but after deploying to production, then the user IP will be returned.