The dreaded "400: redirect_uri_mismatch" error is a common headache for developers working with OAuth 2.0 and OpenID Connect (OIDC). This error signifies a mismatch between the redirect URI you specified in your application's configuration and the redirect URI the authorization server (like Google, Facebook, or Auth0) expects. Let's break down why this happens and how to fix it.
Understanding the Redirect URI
The redirect URI is a crucial part of the OAuth 2.0 authorization flow. It's the URL where the authorization server redirects your user's browser after they successfully (or unsuccessfully) authenticate. This URL needs to be pre-registered with the authorization server during your application's setup. The server uses this to verify that the response is intended for your application and not a malicious actor.
A mismatch occurs when the URI the authorization server uses for redirection doesn't exactly match what you've registered. Even a tiny difference, like a trailing slash or a different port, can trigger this error.
Common Causes and Solutions (based on Stack Overflow insights)
Let's analyze some common scenarios from Stack Overflow, adding context and practical examples:
Scenario 1: Trailing Slash Discrepancy
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Stack Overflow Context: Many posts highlight the issue of a missing or extra trailing slash (
/) in the redirect URI. (Example: Similar questions can be found by searching "redirect_uri_mismatch trailing slash" on Stack Overflow). -
Explanation: The authorization server treats
https://myapp.comandhttps://myapp.com/as distinct URIs. Ensure consistency in your registered URI and the one used in your application's code. -
Example:
- Incorrect: Registered URI:
https://myapp.com, Code uses:https://myapp.com/ - Correct: Both registered and code URI:
https://myapp.comor both:https://myapp.com/
- Incorrect: Registered URI:
Scenario 2: HTTP vs. HTTPS
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Stack Overflow Context: Developers often encounter this issue when mixing HTTP and HTTPS. (Search terms: "redirect_uri_mismatch http https" on Stack Overflow)
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Explanation: The protocol (HTTP or HTTPS) is a critical part of the URI. If your application uses HTTPS, your registered URI must also use HTTPS.
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Example:
- Incorrect: Registered URI:
http://myapp.com, Code uses:https://myapp.com - Correct: Both registered and code URI:
https://myapp.com
- Incorrect: Registered URI:
Scenario 3: Port Mismatch
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Stack Overflow Context: Using a non-standard port (other than 80 for HTTP or 443 for HTTPS) requires precise matching. (Search for "redirect_uri_mismatch port" on Stack Overflow)
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Explanation: If your application runs on a specific port (e.g., 3000 for development), that port number must be included in both the registered and used URIs.
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Example:
- Incorrect: Registered URI:
https://myapp.com, Code uses:https://myapp.com:3000 - Correct: Both registered and code URI:
https://myapp.com:3000
- Incorrect: Registered URI:
Scenario 4: Incorrect Callback URL in Application Settings
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Stack Overflow Context: This error often stems from simply entering the wrong callback URL in your application's settings on the authorization server's platform.
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Explanation: Double and triple check the URL you've entered in the settings of your Google Cloud Console, Facebook Developer portal, Auth0 dashboard, or whichever platform you are using. Many platforms have strict requirements for valid URLs.
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Example: Carefully compare the URL you entered in your application's settings with the one you are using in your application code. Make sure there are no typos.
Preventing redirect_uri_mismatch
- Careful Configuration: Meticulously verify the redirect URI in your application's settings and code.
- Testing: Thoroughly test your application in various environments (development, staging, production).
- Version Control: Use version control (like Git) to track changes to your redirect URI configuration and code.
- Logging: Implement robust logging to capture the actual redirect URI used during the authentication flow. This will help in debugging.
By understanding these common pitfalls and diligently following best practices, you can significantly reduce the chances of encountering the frustrating redirect_uri_mismatch error. Remember to always consult the documentation of your specific OAuth 2.0/OIDC provider for detailed instructions on configuring redirect URIs.