Callback Handler

Overview

What does Callback Handler mean?

Callback Handler is the server-side component that receives, validates, records, and processes callback requests.

How it works in practice

A callback handler is the server endpoint that receives event notifications from a payment gateway or other provider. It should validate transport security, provider identity and any cryptographic signature, parse a documented schema, enforce timestamp or replay limits where supported, and persist accepted events before acknowledging them. The handler should queue expensive processing, then fetch authoritative payment details when an event cannot alone establish final state. Each event needs a trace ID and safe retry semantics.

Further operational details

A typical implementation works as follows: The handler reads the raw request, verifies authenticity, validates the schema and identifiers, records the event durably, acknowledges, and dispatches processing. Replay of Callback Handler should preserve original identifiers and timestamps so historical processing cannot masquerade as a new event.

Core controls require teams to separate receipt from processing, authenticate first, validate amounts and state, deduplicate, use transactions or queues, and preserve audit evidence. For Callback Handler, the event identifier, signature result, delivery attempt, and resulting business state should remain connected throughout processing.

Limits and common misunderstandings

The callback body is untrusted until verified. A public endpoint receiving `paid: true` must not ship goods without validating the provider and order ownership. Duplicate callbacks, delayed statuses and temporary downtime should be expected rather than treated as anomalous surprises.

Related glossary terms

Callback URL; Callback Verification; Callback Retry