Apier.no Subscriptions API
Pro-tier change-detection webhook subscriptions. Consumers register a webhook URL + filter; Apier fires HMAC-SHA256-signed deliveries when matching change-archive events appear. SSRF-resistant (private CIDRs incl. RFC 6598 CGNAT, .local / .internal suffixes, 169.254.x.x metadata endpoints, IPv4-mapped IPv6, trailing-dot FQDN spellings — all blocked at create AND delivery time); the TCP connection pins the validator-approved IP so a hostile DNS server can't substitute a private address between validate and connect; 7-attempt exponential backoff (initial + retries at 1m / 5m / 15m / 1h / 6h / 24h) before abandonment; auto-disables after 6 consecutive 4xx (excluding 408 / 429). Webhook secrets are returned ONCE on creation and stored encrypted-at-rest with key-version support.