A JSON web token(JWT) is JSON Object which is used to securely transfer information over the web(between two parties). It can be used for an authentication system and can also be used for information exchange.The token is mainly composed of header, payload, signature. These three parts are separated by dots(.). JWT defines the structure of information we are sending from one party to the another, and it comes in two forms – Serialized, Deserialized. The Serialized approach is mainly used to transfer the data through the network with each request and response. While the deserialized approach is used to read and write data to the web token.
JWT in the deserialized form contains only the header and the payload.Both of them are plain JSON objects.
A header in a JWT is mostly used to describe the cryptographic operations applied to the JWT like signing/decryption technique used on it. It can also contain the data about the media/content type of the information we are sending.This information is present as a JSON object then this JSON object is encoded to BASE64URL. The cryptographic operations in the header define whether the JWT is signed/unsigned or encrypted and are so then what algorithm techniques to use. A simple header of a JWT looks like the code below:
The ‘alg’ and ‘typ’ are object key’s having different values and different functions like the ‘typ’ gives us the type of the header this information packet is, whereas the ‘alg’ tells us about the encryption algorithm used.Note: HS256 and RS256 are the two main algorithms we make use of in the header section of a JWT. Some JWT’s can also be created without a signature or encryption. Such a token is referred to as unsecured and its header should have the value of the alg object key assigned to as ‘none’.
The payload is the part of the JWT where all the user data is actually added. This data is also referred to as the ‘claims’ of the JWT.This information is readable by anyone so it is always advised to not put any confidential information in here. This part generally contains user information. This information is present as a JSON object then this JSON object is encoded to BASE64URL. We can put as many claims as we want inside a payload, though unlike header, no claims are mandatory in a payload. The JWT with the payload will look something like this:
The above JWT contains userId,iss,sub,and exp. All these play a different role as userId is the ID of the user we are storing, ‘iss’ tells us about the issuer, ‘sub’ stands for subject, and ‘exp’ stands for expiration date.
all these three components make up the serialized JWT. We already know what header and payload are and what they are used for.Let’s talk about signature.
This is the third part of JWT and used to verify the authenticity of token. BASE64URL encoded header and payload are joined together with dot(.) and it is then hashed using the hashing algorithm defined in a header with a secret key. This signature is then appended to header and payload using dot(.) which forms our actual token header.payload.signature
So all these above components together are what makes up a JWT. Now let’s see how our actual token will look like:
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OAuth Vs JWT | What is the difference? | Tech Primers
Q: What is need for JWT?
Q: What are the advantages of JWT?
JWT Token is a popular authentication method used by many web applications. When applying for a position that involves working with JWT Token, it is important to be prepared to answer questions about this authentication method. In this article, we review some of the most common JWT Token questions and provide guidance on how to answer them.
There are no size limitations on the data that can be stored in a JWT, but keep in mind that the larger the data, the larger the token will be. This can impact performance, so it is something to keep in mind when deciding what data to include in a JWT.
JWTs offer a number of advantages over other forms of authentication, such as cookies or sessions. They are easy to use and implement, they are stateless, and they are more secure because they are signed and can be verified. JWTs can also be used to store additional information about the user, such as their permissions or roles.
There is no one-size-fits-all answer to this question, as the best option for you will depend on your specific needs and preferences. However, some reasons you might prefer JWT over other options include its compact size (which makes it ideal for sending over the internet), its support for multiple signature algorithms, and its built-in expiration mechanism.
A JWT is a JSON Web Token, which is used to provide authentication and authorization for users accessing a web application. JWTs are typically used to store user information, such as name and email address, and are signed with a secret key to prevent tampering. When a user tries to access a protected resource, the JWT is sent to the server to be verified. If the JWT is valid, then the user is granted access to the resource.
Store Data in the JWT
With a cookie based approach, you simply store the session id in a cookie. JWTs, on the other hand, allow you to store any type of metadata, as long as its valid JSON. The JWT spec specifies different types of claims that can be included such as reserved, public and private. You can learn more about the specifics and the differences between the types of claims on the jwt.io website.
In practice, what this means is that a JWT can contain any type of data. Depending on your use case you may choose to make the minimal amount of claims such as the user id and expiration of the token, or you may decide to include additional claims such as the users email address, who issued the token, scopes or permissions for the user, and more.
When using the cookie-based authentication, the back-end has to do a lookup, whether that be a traditional SQL database or a NoSQL alternative, and the round trip is likely to take longer compared to decoding a token. Additionally, since you can store additional data inside the JWT, such as the users permission level, you can save yourself additional lookup calls to get and process the requested data.
For example, say you had an API resource /api/orders that retrieves the latest orders placed via your app, but only users with the role of admin have access to view this data. In a cookie based approach, once the request is made, youd have one call to the database to verify that the session is valid, another to get the user data and verify that the user has the role of admin, and finally a third call to get the data. On the other hand, with a JWT approach, you can store the user role in the JWT, so once the request is made and the JWT verified, you can make a single call to the database to retrieve the orders.
The biggest disadvantage of token authentication is the size of JWTs. A session cookie is relatively tiny compared to even the smallest JWT. Depending on your use case, the size of the token could become problematic if you add many claims to it. Remember, each request to the server must include the JWT along with it.
With token-based auth, you are given the choice of where to store the JWT. Commonly, the JWT is placed in the browsers local storage and this works well for most use cases. There are some issues with storing JWTs in local storage to be aware of. Unlike cookies, local storage is sandboxed to a specific domain and its data cannot be accessed by any other domain including sub-domains. Because localStorage works on same-origin policy. So, data stored will only be available on the same origin.
You can store the token in a cookie instead, but the max size of a cookie is only 4kb so that may be problematic if you have many claims attached to the token. Additionally, you can store the token in session storage which is similar to local storage but is cleared as soon as the user closes the browser.
Protecting your users and servers is always a top priority. One of the most common concerns developers have when deciding on whether to use token-based authentication is the security implications. Two of the most common attack vectors facing websites are Cross Site Scripting (XSS) and Cross-Site Request Forgery (XSRF or CSRF).
Cross Site Scripting) attacks occur when an outside entity is able to execute code within your website or app. The most common attack vector here is if your website allows inputs that are not properly sanitized. If an attacker can execute code on your domain, your JWT tokens are vulnerable.
XSS attacks are much easier to deal with compared to XSRF attacks because they are generally better understood. Many frameworks, including Angular, automatically sanitize inputs and prevent arbitrary code execution. If you are not using a framework that sanitizes input/output out-of-the-box, you can look at plugins like caja developed by Google to assist. Sanitizing inputs is a solved issue in many frameworks and languages and I would recommend using a framework or plugin vs building your own.
On the other hand, if your use case requires you to store the JWT in a cookie, you will need to protect against XSRF. XSRF are not as easily understood as XSS attacks. Luckily, preventing XSRF attacks is a fairly simple matter. To over-simplify, protecting against an XSRF attack, your server, upon establishing a session with a client will generate a unique token (note this is not a JWT). Then, anytime data is submitted to your server, a hidden input field will contain this token and the server will check to make sure the tokens match. Again, as our recommendation is to store the JWT in local storage, you probably will not have to worry about XSRF attacks.
1> One of the best ways to protect your users and servers is to have a short expiration time for tokens. That way, even if a token is compromised, it will quickly become useless.
2> Additionally, you may maintain a blacklist of compromised tokens and not allow those tokens access to the system.
3> Finally, the nuclear approach would be to change the signing algorithm, which would invalidate all active tokens and require all of your users to log in again. This approach is not easily recommended, but is available in the event of a severe breach.
FAQ
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