SSRF Canary Callback Server
==========================
Register (use in SSRF payload):
  http://ssrf.noxian.io/canary/<canary>
  http://ssrf.noxian.io/canary?c=<canary>
Any HTTP method registers the canary. <canary> = any string (UUIDv4 by convention).

Check if it was hit:
  https://ssrf.noxian.io/?canary=<canary>
  https://ssrf.noxian.io/check/<canary>?json=1   (full hit details)
Returns: HIT <canary> count=N ...  /  MISS <canary>

Other:
  /list       all stored canaries (canary + count + first/last seen)
  /healthz   200 ok
  /           this help

Canaries auto-expire after 5 hours. Storage: /var/lib/ssrf-canary