8/22/2023 0 Comments Decode jwt payload![]() ![]() We have created our JWT, how can we now verify and decode the token when it is passed between the server and the client?įirst, we split the token string into three parts, when we created the token remember we attached the encoded headers to the encoded payload and finally to the signature using a period as a delimiter. The digest function will consume the HMAC and return to us the calculated digest of the value passed into the update function in an encoded string in the format passed into it, in this example we use the base64url to ensure that our JWT is URL-Safe. We call update on the HMAC object returned from the createHmac function to add the data we want to store in it, when we are done we call digest on it. The signature is created by calling the createHmac function, we use the sha256 hashing algorithm, this information should also be contained in the alg property of the header, however sha256 is not the only algorithm that can be used, JWTs support other hashing algorithms. Thus it is not wise to store any sensitive information in the payload. Let's write the function that allows us to create a signature.Įnter fullscreen mode Exit fullscreen modeįrom the code block above, we can decipher that a JWT has three parts, the encoded header, the encoded payload, and the signature, if you are familiar with your javascript you know that the information in the header and the payload can easily be constructed. The secrete can be shared between a client and server if need be, but most of the time it should just be kept on the server. This method accepts two parameters, a hashing algorithm and a secrete, This secrete is what is used to validate the authenticity of our JWT. To create one we need the crypto module that comes baked in with Node JS, the crypto module exposes a function createHmac function that allows us to create one. You should know that a JWT is an implementation of an HMAC Hash-Based Message Authentication Code. Visit Netcreed to read more articles like this We will move to use a standard JWT library and practical applications JWTs in an application. In this article, we will see a basic implementation of JWTs to understand how they work under the hood. The payload in a JWT will usually contain one or more claims that define the level of authorization allocated to the user. ![]() A JWT is used for authorization and lightweight authentication. A JWT is signed with a private key and/or public key and is URL-safe, this implies that a JWT doesn't have unencoded / or ? or & characters. Jsonwebtokens or JWT as they are otherwise known is an open standard for creating a data signature that contains a payload in JSON format. ![]()
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