What Is JWT? A Beginner’s Guide to JSON Web Tokens
If you’re someone who struggles with messy authentication solutions or worried about keeping user data secure, you’re not alone. Fortunately, JSON Web Tokens better known as JWTs offer a clean, simple way to handle authentication across your apps. This tiny, URL-friendly token format has completely changed how developers build secure login systems.
In this blog, we’ll break down how JWTs work and why they’ve become such a popular choice for modern web applications.
What Is JWT?
JWT (JSON Web Token) and often pronounced “jot”; is an open standard that allows you to create small, self-contained tokens for securely sharing information between applications or services. These tokens are especially useful for authentication and authorization because they can carry details that confirm who a user is and what they’re allowed to do.
When it comes to authentication, a JWT helps a server quickly decide whether it can trust a client it has never seen before. By embedding verified information inside the token, JWTs make the entire login process faster, safer, and easier to manage across modern applications.
Structure of a JWT
A JWT consists of three components, separated by dots (.):
Header.payload.signature
Let’s look at each part:
1. JWT Header (Image Required))
The header tells the system what type of token it is and which algorithm is being used to sign it.
A typical JWT header looks like this:
{
“alg”: “HS256”,
“typ”: “JWT”
}
- alg = signing algorithm
- typ = token type (always JWT)
It’s then Base64URL-encoded before being added to the token.
2. JWT Payload
The JWT payload contains the claims; the actual data being sent. It mainly includes user information, permissions, and token metadata.
Common claim types include:
- iss – Issuer
- sub – Subject (usually the user ID)
- exp – Expiration time
- iat – Issued at
- aud – Intended audience
Example payload:
{
“sub”: “1234567890”,
“name”: “John Doe”,
“role”: “admin”,
“exp”: 1712345678
}
This section is also Base64URL-encoded.
3. JWT Signature
JWT signature ensures the token hasn’t been tampered with.
The signature is created by taking:
Base64UrlEncode(header) + “.” + Base64UrlEncode(payload)
and signing it with:
- a secret key (for HS256), or
- a private key (for RS256/ES256)
Example:
HMACSHA256(
base64UrlEncode(header) + “.” + base64UrlEncode(payload),
your-secret-key
)
If the signature doesn’t match when the server checks it, the token is rejected.
Putting It All Together
A full JWT looks like:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.
eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvbiBEb2UiLCJyb2xlIjoiYWRtaW4ifQ.
SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
Three parts. Three purposes:
- Header → Identifies the token.
- Payload → Carries the data.
- Signature → Ensures integrity.
How Does JWT Work?
Here are the key points on how JWT works:
- User Login – The user signs in through your app; whether it’s on the web or mobile by entering their username and password.
- Server Creates a JWT – Once the credentials are verified, the server generates a JWT using a secure secret key.
- Token Sent to the Client – The server sends this newly created token back to the client, where it can be stored for future use.
- Authenticated Requests – From this point on, every time the client needs access to a protected resource, it simply includes the JWT in the request. The server checks the token’s validity and, if everything looks good, grants access.
When and Where to Use JWT?
JWTs shine in scenarios where you need secure, stateless, and scalable authentication across different applications or devices.
Below is when and where they make the most sense:
- Stateless Authentication (No Server-Side Sessions)
Use JWT when you want to avoid storing session data on the server. Because JWTs are self-contained, they allow you to authenticate users without keeping session records which is perfect for highly scalable systems.
- Single Page Applications (SPAs)
Frameworks like React, Angular, and Vue pair extremely well with JWT because:
- They rely heavily on APIs.
- They don’t use traditional server-side sessions.
- They often run in distributed environments.
- Microservices & Distributed Systems
JWTs are ideal in microservice architectures because:
- Each service can validate the token independently.
- No centralized session store is needed.
- Tokens can move between services securely.
Helps decrease latency and simplifies communication.
- APIs and Mobile Applications
JWTs are compact and easily transmitted over HTTP headers, making them perfect for:
- REST APIs
- Mobile apps
- IoT devices
- Third-party integrations
Their small size also reduces bandwidth usage.
- Single Sign-On (SSO)
JWT is widely used in SSO systems because:
- It works across domains.
- It’s easy to pass between different apps.
- It can contain identity + authorization information.
Many enterprise SSO solutions rely on JWT under the hood.
- Temporary Access or Scoped Permissions
JWTs can include custom claims like:
- Roles
- Permissions
- Token expiration
- Allowed actions
This makes them useful for:
- Granting temporary access
- Role-Based Access Control (RBAC)
- Restricting API access
JWT Authentication Example
Here’s a simple look at how JWT fits into an authentication flow:
- The user logs in by submitting their username and password to the server for authentication.
- The server checks the credentials, and if everything is correct, it creates a JWT that includes the user’s details as claims and signs it is using a secure secret key.
- The server returns the JWT to the user as part of the response.
- The user stores the token that’s typically in local storage or a cookie and then includes the JWT in the Authorization header for every request that requires authentication.
- For each new request, the server decodes the incoming JWT and verifies its signature. If the token is valid, the server trusts the identity, processes the request, and delivers the appropriate response.
This flow keeps authentication fast, secure, and completely stateless making it ideal for modern web applications.
JWT Advantages
JWTs offer much more than just scalability and a stateless design.
Below we will discuss about what are some compelling reasons to consider:
- Cross-domain friendly – Unlike traditional cookies, JWTs work seamlessly across different domains and subdomains. This makes them a perfect fit for Single Sign-On (SSO) systems where users need to move effortlessly between multiple apps.
- Self-contained and flexible – Each JWT carries the essential user information inside the token itself, eliminating the need for repeated database lookups. You can also add custom claims to include any additional data you need, giving you tremendous flexibility in how you structure your authentication flow.
- Great for mobile apps – JWTs are lightweight and stateless, they’re ideal for mobile authentication. They work smoothly with APIs and help reduce unnecessary server load, which can significantly boost performance in mobile environments.
- Stronger security options – JWTs can be encrypted to protect sensitive information, ensuring only the intended recipients can read the token. Their digital signatures also guarantee that the token hasn’t been altered during transmission, providing an extra layer of trust and integrity.
JWT Disadvantages
Here are some of the key limitations you should be aware of when using JWT:
- Hard to revoke – Once issued, a JWT stays valid until it expires, which can make immediate revocation challenging.
- Risk if the secret key is exposed – If your signing key is ever compromised, attackers could potentially create their own valid tokens.
- Larger token size – Because JWTs contain JSON data, they’re generally bigger than simple opaque tokens, which can add some overhead in certain environments.
Best Practices for Keeping JWTs Secure
If you are looking for rock-solid, enterprise-grade authentication, start here. The following essential points outline the best practices for building and managing secure JSON Web Tokens:
- Protect your secret key – The secret key used to sign your JWTs is the heart of your security. Keep it strictly confidential. Store it in a secure environment variable or, even better, use a dedicated key management system to prevent unauthorized access.
- Always use HTTPS – To ensure your tokens aren’t intercepted or tampered with during transmission, make sure all communication between the client and server happens over HTTPS. This simple step dramatically reduces the risk of token theft.
- Choose strong signing algorithms – The security of your application heavily depends on the algorithm you use to sign your JWTs. Asymmetric algorithms like RSA or ECDSA offer stronger protection because they rely on a public/private key pair, making it extremely difficult for attackers to forge tokens.
- Plan for token revocation – JWTs should have short expiration times to limit the damage if a token is compromised. In addition, make sure your system supports token revocation especially in high-risk scenarios like account deletion, compromised credentials, or security incidents.
What Is OAuth?
OAuth (Open Authorization) is an open standard that makes it easy for web, mobile, and desktop applications to request access securely. Think of it like giving someone a valet key to your car: they can drive and park it, but they don’t get full control. In the same way, OAuth lets apps access only the specific information or actions you approve, without ever sharing your full credentials.
How OAuth Works?
OAuth works by letting a trusted service handle user authentication while allowing third-party applications to access only the information the user approves.
- Here’s the process in a simple, easy-to-follow flow:
- The user starts the process by trying to access something in the application.
- The application sends the user to the OAuth provider (like Google, Facebook, or GitHub) for authentication.
- The user logs in with the OAuth provider using their existing account.
- The OAuth provider asks for consent and confirms what the application is requesting access to.
- The user approves the request and grants the application limited access.
- The OAuth provider returns an authorization code back to the application.
- The application exchanges that code for an access token, which proves it has permission.
- The application uses the access token to access the protected resources on the user’s behalf.
This flow keeps user credentials secure, gives users full control over what they share, and makes authorization both safe and seamless.
When and Where to Use OAuth?
OAuth is designed for situations where users need to grant limited access to their data without sharing their password. It’s ideal anytime one application needs permission to act on behalf of a user in another system. Here’s when and where OAuth fits best:
- Third-Party App Authorization
Use OAuth when you want users to log in or connect using accounts from trusted providers like:
- GitHub
- Microsoft
Example:
“Login with Google” or connecting your app to a user’s Dropbox files.
- Accessing User Data from External Services
OAuth is perfect when your application needs to access user data stored somewhere else with the user’s permission.
Examples:
- A calendar app accessing Google Calendar events.
- A CRM pulling contacts from Office 365.
- A fitness app fetching user data from Fitbit.
- Mobile, Web, and Desktop Appsthat Avoid Handling Passwords
OAuth removes the need for your application to store or manage user passwords, which significantly reduces security risk.
Great for:
- Single-Page Apps (SPAs)
- Native mobile apps
- Desktop applications
- Browser extensions
- APIs That Require Authorization
When building or consuming APIs, OAuth provides a secure way to issue access tokens that define exactly what the client can access.
Examples:
- REST APIs
- GraphQL APIs
- Microservices needing delegated access
- Single Sign-On (SSO) Implementations
OAuth (and OpenID Connect on top of it) is widely used in SSO systems because it:
- Let’s users authenticate once.
- Allows access across multiple independent applications.
- Improves user experience and reduces password fatigue.
Can OAuth and JWT Be Used Together?
Absolutely!! OAuth and JWT not only work well together, but they’re also often the perfect match. OAuth 2.0 can issue JWTs as access tokens, combining OAuth’s powerful authorization framework with the simplicity and portability of JWTs.
Pointers below highlights how OAuth and JWT complement each other:
- OAuth manages the authorization process and decides whether a user or app should have access.
- The access token issued by OAuth can be a JWT, packed with claims about the user and their permissions.
- The resource server can verify the JWT on its own, without having to check back with the authorization server every time.
This approach delivers several major benefits:
- Less strain on your authorization server.
- Faster performance across distributed APIs and microservices.
- Strong security thanks to JWT’s built-in signature validation.
JWT vs OAuth: Comparison Table
Below table represents in what ways JWT and OAuth are different from each other:
| Feature / Aspect | JWT (JSON Web Token) | OAuth (Open Authorization) |
|---|---|---|
| Purpose | Provides a compact, self-contained token for authentication & authorization. | Allows third-party apps to gain limited access to a user’s resources without sharing credentials. |
| Function | Encodes user data inside the token (claims). | Manages the entire authorization flow and issues tokens. |
| Token Type | JWT is a format (header.payload.signature). | OAuth tokens can be JWTs or opaque tokens depending on implementation. |
| Statefulness |
Completely stateless server does not store session data. |
OAuth itself can be stateful or stateless, depending on token type and architecture. |
| Data Storage | Contains claims directly in the token. | Stores authorization decisions or scopes at the provider level. |
| Security Focus |
Token integrity (signatures), expiration, and claim verification. |
User consent, delegated access, and secure authorization flows. |
| Validation | Verified locally by checking the signature no server lookup needed. | Often requires communication with the authorization server (except when JWT is used). |
Conclusion
JSON Web Tokens (JWTs) are one of the go-to tools for modern authentication because they are simple to use, easy to share between systems, and do not require server-side sessions. For beginners, understanding how JWTs work, along with their structure, benefits, and best practices, opens the door to building more secure and scalable applications. Whether you work with web apps, mobile APIs, or microservices, JWTs offer a clean way to transmit user identity and permissions without server-side sessions.
One of the biggest strengths of JWTs is their role in Single Sign-On (SSO). Because they easily travel across domains and services, JWTs make it possible for users to log in once and access multiple applications seamlessly. This capability improves the user experience and reduces the complexity of managing authentication across distributed systems.
JWTs are more than just a token format. They serve as a powerful tool for building secure, efficient, and user-friendly authentication flows.
FAQs
What are JWT tokens?
JWT tokens are small, secure pieces of information that a server creates and sends to a user after they log in.
What does JWT full form mean?
The JWT full form is JSON Web Token. It is a compact, URL-safe format used to transmit verified data between a client and server.
What is JWT tokenization?
JWT tokenization refers to the process of turning user identity and permissions into a digitally signed JWT token.
What is the JWT structure?
The JWT structure has three parts:
- Header – specifies the signing algorithm
- Payload – contains user data and claims
- Signature – verifies that the token hasn’t been changed
Together, they form a string like: header.payload.signature.
What happens when a JWT expires?
When a JWT expires, the client must obtain a new one usually by using a refresh token or logging in again. Expiration prevents long-term token misuse.
Why use JWT?
JWT provides a secure, tamper-proof way to share identity information between services.
How to generate JWT token?
To understand how you create JWT token, you combine a header, payload, and a secret key (or private key) and encode them using a chosen signing algorithm like HS256 or RS256. Most frameworks provide libraries that handle the process automatically.
What is JWT for authentication?
JWT for authentication means using a token to identify a user without storing session data on the server.
What can be an example of a JSON Web Token example?
Here’s a simple JSON Web Token example:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
.eyJ1c2VySWQiOiIxMjMiLCJyb2xlIjoiYWRtaW4ifQ
.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
This token includes a header, a payload with user claims, and a signature.
JWT explained in simple terms and how does it work?
You log in → the server creates a signed token → you send that token with each request → the server verifies it and grants access. No session storage, no server-side state just fast, stateless authentication.
Are JWTs secure?
JWTs are secure when implemented correctly. While the payload isn’t encrypted by default, the signature prevents tampering.
Where are JWTs stored?
JWTs can be stored in:
- Local storage
- Session storage
- Cookies
- Memory (recommended for high-security environments)
Each method has different security considerations.
