Override a `Set-Cookie` header with a certain value

export default {
    async fetch(request) {
        // Receive response from the origin
        const response = await fetch(request)

        // Create a new Headers object to modify response headers
        const newHeaders = new Headers(response.headers);

        // Get all Set-Cookie headers
        const cookies = response.headers.get("Set-Cookie");
        if (cookies) {
            // Split the Set-Cookie headers
            const cookieArray = cookies.split(/,(?=\s*[^;]+=[^;]+)/g);
            const updatedCookies = cookieArray.map(cookie => {
              // For example, replace the currency value with GBP
                if (cookie.trim().startsWith("currency=")) {
                    return cookie.replace(/currency=[^;]+/, "currency=GBP");
                }
                return cookie;
            });

            // Delete the existing Set-Cookie headers
            newHeaders.delete("Set-Cookie");

            // Add the updated Set-Cookie headers individually
            updatedCookies.forEach(cookie => {
                newHeaders.append("Set-Cookie", cookie.trim());
            });
        }

        // Return the modified response with updated headers
        return new Response(response.body, {
            status: response.status,
            headers: newHeaders
        });
    },
};