Verify JWT with Crypto API: Common Issues & Fixes

A step-by-step guide to verifying JSON Web Tokens (JWT) with the Crypto Web API in JavaScript, addressing common pitfalls and providing a working code example.
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This video is based on the question https://stackoverflow.com/q/76315264/ asked by the user 'muell' ( https://stackoverflow.com/u/19526639/ ) and on the answer https://stackoverflow.com/a/76317134/ provided by the user 'muell' ( https://stackoverflow.com/u/19526639/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Verifying A JWT Using the Crypto Web API: Solving Common Issues

JSON Web Tokens (JWTs) are a popular way to securely transmit information between parties. However, verifying these tokens can sometimes be tricky, especially if you're using the Web Crypto API in JavaScript. In this guide, we'll explore a common issue faced when verifying a JWT and how to resolve it efficiently.

Understanding the Problem

When attempting to verify a JWT, you might encounter situations where the verification function always returns false, even with valid tokens. Here’s a simplified version of the code that might have led to this confusion:

[[See Video to Reveal this Text or Code Snippet]]

In this example, the user parameter contains the JWT, and the function is supposed to verify its authenticity using a secret key. However, it has been reported that the function always returns false, which can be frustrating.

The Solution: A simple fix

The main issue with the code lies in how the JWT parts are being joined together. Specifically, the join() method was missing its argument, which is crucial for assembling the original signature. The correct way to join the first two parts of the JWT is to use a period (.) as the separator.

Here’s the corrected code:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Made:

Join Method Correction: The join() function now uses join(".") instead of just join(). This specifies that a period must be used to concatenate the two parts, correctly recreating the original data that was signed.

Conclusion

Verifying JWTs with the Web Crypto API can be straightforward if you pay attention to small details, such as how you piece together your split strings. By ensuring that parameters are correctly formatted, you can successfully verify JWTs without relying on external libraries.

Recap:

Make sure the join() method includes the proper separator.

Always double-check how the token parts are being handled to avoid verification failures.

By following these guidelines, you should be able to confidently verify JWTs in your applications. Happy coding!