public static class GatewayAuthHelper
{
    public const string DevGatewayKey = "dev-gateway-key-change-in-production";

    public static void WithGatewayApiKey(
        this HttpClient client, Guid gatewayId, string? apiKey = null)
    {
        client.DefaultRequestHeaders.Remove("X-Api-Key");
        client.DefaultRequestHeaders.Remove("X-Gateway-Id");
        client.DefaultRequestHeaders.Add("X-Api-Key", apiKey ?? DevGatewayKey);
        client.DefaultRequestHeaders.Add("X-Gateway-Id", gatewayId.ToString());
    }
}