A callback URL is a web address that receives a redirect or data from another application after an event or process finishes. In software, it commonly supports OAuth sign-in, payment updates, and API event notifications. Its exact behavior depends on whether a browser is redirected to it or a service sends it a server-to-server request.
Callback URL
What Is a Callback URL?
A callback URL is a web address that receives a redirect or data from another application after an event or process finishes. An app supplies this endpoint so another system can return a user or send an API result.
How a Callback URL Works
- Your app provides a URL, such as https://app.example.com/auth/callback.
- The external service stores or validates it.
- A user action or background task finishes.
- The service redirects a browser or sends an HTTP request to that endpoint.
Callback URL vs Redirect URL vs Webhook
| Term | Typical use |
|---|---|
| Callback URL | General return or notification endpoint. |
| Redirect URL | Browser return path, often used in OAuth. |
| Webhook | Server-to-server event payload, usually without a browser. |
OAuth Callback URL Example
In OAuth, https://app.example.com/auth/callback must be pre-registered exactly. The provider returns an authorization code and state value; the server validates state, then exchanges the code for tokens.
Callback URL Security Best Practices
- Use HTTPS and exact redirect-URI allowlists.
- Validate OAuth state and webhook signatures.
- Do not log codes, tokens, or secrets.
- Process duplicate deliveries safely.
Practical Limits and Testing Considerations
- URL mismatches and expired state values can stop OAuth sign-in.
- Localhost is not reachable by most external services.
- Use a tunnel or provider-approved local redirect URI for testing.
- Expect retries, timeouts, and duplicate webhook requests.
Callback URLs in Emergent
Emergent can help build full-stack endpoints for authentication, integrations, and event handling. Explore Emergent Learn, the software glossary, and AI tools for coding to plan callback-capable applications. Build integrations that handle callbacks with Emergent.
Frequently Asked Questions
Your Questions, Answered
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What is a callback URL example?
https://app.example.com/auth/callback is a common OAuth callback URL example.
Is a callback URL the same as a redirect URL?
Often, in OAuth. A callback URL is broader, while a redirect URL specifically sends a browser back to an app.
What is a callback URL in OAuth?
It is the registered redirect URI where an identity provider returns the browser after sign-in.
How do I create a callback URL?
Create a route in your application, deploy it with HTTPS, then register its exact URL with the external provider.
How do I test a callback URL locally?
Use a provider-approved localhost URL or a secure tunnel that gives your local app a temporary public HTTPS address.
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