How can I access the Supabase user ID in a SvelteKit +server.ts endpoint for Stripe checkout metadata?

I'm trying to add my Supabase user ID to a Stripe checkout session's metadata, but I can't access it in my +server.ts file using @supabase-ssr in SvelteKit. I already create a Supabase client in my +layout.ts file based on the setup docs, so I shouldn't need to create it again elsewhere.

In one instance, accessing the user ID using event.locals.user inside a +page.server.ts file worked as intended:

JAVASCRIPTCopied
const { data, error } = await supabase
    .from('form_flow_purchases')
    .insert({
        user_id: event.locals.user?.id,
        principal_name: principal,
        state_of_residence: stateOfResidence,
    });

However, in my Stripe checkout session file (+server.ts), trying to use the following results in an error due to a deprecated event:

JAVASCRIPTCopied
const supabase = event.locals.supabase;

Here's the full code for context:

TYPESCRIPTCopied
import Stripe from 'stripe';
import { json, type RequestEvent } from '@sveltejs/kit';
import { BASE_URL, STRIPE_SECRET_KEY } from '$env/static/private';

const stripe = new Stripe(STRIPE_SECRET_KEY);

export async function POST({ request }: RequestEvent) {
    try {
        const supabase = event.locals.supabase; // Error here
        const { priceId } = await request.json();

        const session = await stripe.checkout.sessions.create({
            payment_method_types: ['card'],
            mode: 'payment',
            line_items: [
                {
                    price: priceId,
                    quantity: 1
                }
            ],
            metadata: {
                user_id: /* Need to add user ID here */
            },
            success_url: `${BASE_URL}/payments/success?session_id={CHECKOUT_SESSION_ID}`,
            cancel_url: `${BASE_URL}/payments/cancel`
        });

        return json({ url: session.url });
    } catch (error) {
        console.error('Stripe Checkout Error:', error);
        return json({ error: 'Failed to create checkout session' }, { status: 500 });
    }
}

I suspect the issue is related to destructuring the event improperly, as the function signature only extracts request and not locals. The desired outcome is to correctly access the user ID from locals (i.e., locals.user?.id) so it can be added to the Stripe session's metadata. Any suggestions on resolving this?