How to Decode JWT Tokens using JwtSecurityTokenHandler and Resolve 'string needs to be in compact JSON format' Errors?

Decoding JWT Tokens with JwtSecurityTokenHandler

Decoding JWT tokens can be a straightforward task using the JwtSecurityTokenHandler class. However, if you encounter issues like the "string needs to be in compact JSON format" error, here's how to resolve it.

As mentioned in the question, the JwtSecurityTokenHandler requires the string to be in a specific format: Base64UrlEncodedHeader.Base64UrlEndcodedPayload.OPTIONAL,Base64UrlEncodedSignature.

To resolve this issue, the solution involves casting the result of ReadToken or using the ReadJwtToken method instead. Here's how it works:

Using Cast Method:

var stream = "[encoded jwt]";
var handler = new JwtSecurityTokenHandler();
var jsonToken = handler.ReadToken(stream);
var tokenS = jsonToken as JwtSecurityToken;

The tokenS variable is now of type JwtSecurityToken, allowing access to claims using tokenS.Claims.

Using ReadJwtToken Method:

var token = "[encoded jwt]";
var handler = new JwtSecurityTokenHandler();
var jwtSecurityToken = handler.ReadJwtToken(token);

Alternatively, you can directly read the token using the ReadJwtToken method. This method also returns a JwtSecurityToken object.

Once the token is correctly decoded, you can retrieve claims using:

var jti = tokenS.Claims.First(claim => claim.Type == "jti").Value;

This will retrieve the jti claim value from the token.

Remember, it's essential to use the correct format when decoding JWT tokens with JwtSecurityTokenHandler to avoid errors and ensure proper access to claims.

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