jwt strings must contain exactly 2 period characters. found: 0

3 min read 01-10-2024

jwt strings must contain exactly 2 period characters. found: 0

When working with JSON Web Tokens (JWTs), developers often encounter various validation errors, one of the most common being: "JWT strings must contain exactly 2 period characters. Found: 0." This error can be confusing, especially for those new to JWT. In this article, we will dissect this error, its causes, and how to address it, while providing additional context and practical examples.

What is a JWT?

JWTs are a compact, URL-safe means of representing claims to be transferred between two parties. They are widely used in authentication and information exchange due to their stateless nature. A JWT consists of three parts: the header, the payload, and the signature. Each part is separated by a period (.).

A standard JWT looks like this:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

In this example, the JWT contains the header, payload, and signature separated by two periods.

Causes of the Error

When the error message states that there are "0 period characters," it implies that the string provided to the JWT validator does not contain the expected structure. Possible causes for this issue include:

Malformed JWT: The token string may not be formatted correctly, resulting in missing sections or extra characters.
Empty String: An empty string is being passed instead of a valid JWT.
Improper Token Generation: The code or library used to generate the JWT may not be functioning correctly, leading to an incorrectly formatted token.

Practical Example of the Error

const jwt = require('jsonwebtoken');

const token = ""; // Empty string leads to the error
const secretKey = "your-256-bit-secret";

try {
    const decoded = jwt.verify(token, secretKey);
    console.log(decoded);
} catch (err) {
    console.error(err.message); // JWT strings must contain exactly 2 period characters. Found: 0
}

In this example, passing an empty string as a JWT to the verify function triggers the error message.

How to Fix the Error

To resolve this error, you can follow these steps:

Check the JWT Format: Ensure that the JWT string has the correct format: three base64url-encoded strings separated by periods. For example:
```
const validJwt = "header.payload.signature";
```

Verify Token Generation: If you are generating the JWT yourself, ensure that your implementation is correct. Utilize libraries like jsonwebtoken for Node.js to create JWTs reliably.

const jwt = require('jsonwebtoken');

const payload = { userId: 12345 };
const secretKey = "your-256-bit-secret";
const token = jwt.sign(payload, secretKey);
console.log(token); // This will log a valid JWT

Implement Error Handling: Always implement error handling when decoding or verifying JWTs to catch and respond to issues more gracefully.

try {
    const decoded = jwt.verify(token, secretKey);
} catch (err) {
    if (err.message === "jwt malformed") {
        console.error("The provided token is malformed. Please check the token.");
    } else {
        console.error(err.message);
    }
}

Conclusion

Understanding the structure and requirements of JWTs is crucial for avoiding common pitfalls in their usage. The error "JWT strings must contain exactly 2 period characters. Found: 0" signifies a problem with the JWT format, typically due to malformed tokens or empty strings. By following the recommendations and examples outlined in this article, you can efficiently debug and correct these issues, ensuring a smooth experience when implementing JWTs in your applications.

Additional Resources

For further reading, consider the following resources:

By equipping yourself with knowledge about JWTs and their validation, you can enhance your authentication mechanisms and build secure applications.