Builds a signed sandbox checkout URL with real credentials. It never movesmoney: the URL is printed for a manual visit, which is enough to confirm thesignature pipeline end to end.
Run it with environment variables set (all three are required; without themthe command prints what to set and exits):
Then open the printed URL in a browser — the Alipay sandbox cashier shouldrender. Sandbox gateway and credentials come from the Alipay open platform(https://open.alipay.com → 沙箱环境).