Introduction to JWT
JSON Web Token (JWT) is a compact, URL-SAFE mechanism for securing claims between two parties. Defined by Open Standard RFC 7519, JWTS encapsulates information as a JSON object, which can be verified and reliable due to its digital signature. This signature ensures data integrity and authenticity to prevent tampering during transmission.
JWTS can be signed using a secret key (HMAC algorithm) or a public/private key pair (RSA or ECDSA), making them highly versatile for authentication and authorization. They are widely used in web protection, enabling secure stateless authentication in API, single sign-on (SSO), and Microservices Architecture. Their mild nature makes them ideal for transmitting information efficiently across distributed systems.
Why is JWT Used?
JWT is widely used for authentication and authorization in modern web applications and APIs due to its efficiency, safety, and scalability. It enables stateless authentication, eliminating the requirement of continuous database lookups, which improves performance and reduces server load. Since JWTs are self-contained, they store all essential user information, such as identity, roles, and permissions, making them ideal for implementing single sign-on (SSO) in many applications.
In addition, JWTS enhances security by ensuring data integrity through cryptographic signatures, preventing tampering and unauthorized modifications. They can be signed using HMAC (shared secret) or asymmetric encryption (RSA/ECDSA), which adds a layer of protection against token forgery. Their compact and URL-safe format makes them perfect for web, mobile, and microservices-based applications, which facilitates seamless authentication across distributed systems.
Structure of a JWT
A JSON web token (JWT) is a compact and self-contained token for secure information exchange. It consists of three parts, separated by dots (.), Which simultaneously enable authentication and authorization to ensure data integrity. Each component plays an important role in the functionality of tokens:
Header
The header contains metadata about the token, including the type (JWT) and the signing algorithm used, such as HS256 (HMAC SHA-256) or RS256 (RSA with SHA-256). This helps the system understand how to process and verify the token securely.
Payload
The payload contains claims, which are key-value pairs representing data about the user or entity. These claims may be registered claims (e.g., ISS for issuer and exp for expiry time), public claims (custom data shared within the system), or private claims (specific to an application). Since JWTs are self-contained, all necessary user information is stored here, reducing reliance on the database.
Signature
The signature ensures the token’s authenticity and integrity. It is created by encoding the header and payload using Base64Url and then signing the result with a secret key (HMAC) or private key (RSA/ECDSA). This prevents tampering, as any unauthorized modification invalidates the token.
Example of a JWT structure: [
Header.Payload.Signature ] 
Types of JWT Claims
JWT claims that the information inside a token is defined and provides details about the entity being authenticated. They are classified into three types, each serving a different purpose:
Registered Claims
These are predetermined claims defined by JWT standards, including iss (issuer), exp (expiry time), sub (subject), and aud (audience). They help standardize token information and improve interoperability in the system.
Public Claims
Public claims are customized claims that any application can use, provided they are unique to preventing conflicts. They allow developers to include further relevant data for token processing.
Private Claims
Private claims are custom claims that are shared between specific parties for cases of specific use only. These are usually used for internal application needs and are not standardized like registered claims.
How JWT Works
JWT ensures secure authentication and authorization by enabling the exchange of verified user information. The process includes the following steps:
User Authentication
The user signs in using valid credentials, including a username and password.
Token Generation
The authentication server verifies the credentials and generates a JWT that contains user details and claims.
Token Storage
The JWT is sent to the client and stored securely in either local storage, session storage or HTTP-only cookies.
API Requests
The client includes the JWT in the authorization header of API requests, confirming authentication.
Token Verification
The server checks the JWT’s signature and claims before granting access to protected resources. If the token is valid, the request will be processed.
Advantages of JWT
JWTs offer numerous advantages, which makes them a popular choice for authentication and authorization in modern applications:
Compact and Efficient
JWTs are small in size and encoded in Base64Url, enabling easy transmission through URLs, headers, and cookies without excessive bandwidth consumption.
Stateless Authentication
Since JWTs are self-contained, they remove the necessity for server-side session storage, which lessens database queries and enhances scalability.
Security
JWTs guarantee data integrity with cryptographic signatures via HMAC, RSA, or ECDSA, preventing unauthorized tampering.
Cross-Domain Support
JWTs are perfect for Single Sign-On (SSO) and distributed systems, permitting seamless authentication across various applications and domains.
Security Considerations of JWT
While JWT improves security, improper implementation can create vulnerabilities. Adhering to best practices is essential for mitigating risks.
Use HTTPS
Always transmit JWTs over HTTPS to thwart interception via man-in-the-middle (MITM) attacks.
Short-Lived Tokens
Set expiration times (exp) for JWTs and use refresh tokens to reduce exposure in case a token is compromised.
Secure Storage
Avoid storing JWTs in local storage to prevent Cross-Site Scripting (XSS) attacks; instead, rely on HTTP-only cookies for enhanced security.
Token Validation
Always verify JWT signatures and claims on the server before processing requests to ensure token authenticity and prevent unauthorized access.
JWT vs. Session-Based Authentication
The Role of JWT in Modern Authentication
JWT is a powerful and widely adapted solution for authentication and authorization and offers a compact, effective, and secure method for transferring user information. The stateless nature eliminates the need for increased storage on the server side, making it ideal for scalable applications, APIs, and microservices. JWT’s ability to store important user information in the token itself enables seamless authentication, especially in single-order (SSO) environments.
However, although JWT improves safety through cryptographic signatures, incorrect implementation can introduce risks such as token -theft, replay attacks, and exposure to XSS or CSRF vulnerabilities. To fully utilize JWT’s benefits, developers must enforce best practices such as the use of short-lived tokens, secure storage mechanisms, and proper validation techniques to prevent unauthorized access and data breaches.
