All You Need to Know About JWT Authentication 

  • By Pooja Ghodekar
  • August 26, 2023
  • MEAN Stack
All You Need to Know About JWT Authentication 

All You Need to Know About JWT Authentication 

All You Need to Know About JWT Authentication. JSON Web Token (JWT) authentication is a method of securely transmitting information between parties as a JSON object.JWTs are compact and self-contained, making them suitable for carrying information such as user identity, roles, and permissions. 

Parts of JWT

Header: Contains metadata about the type of token and the cryptographic algorithms used to secure it. 

Payload: Contains the claims, which are statements about an entity and additional data. Claims can be things like the user’s ID, roles, permissions, expiration time, etc. 

Signature: It’s created by encoding the header, payload, and a secret key with the specified algorithm.  The basic flow of JWT authentication is as follows: 

User Authentication:
The user logs in using their credentials (username and password). 

The server validates the credentials and generates a JWT containing the necessary user information. 

Token Generation:
The server constructs the JWT, including the header and payload.
The payload contains claims such as the user’s ID, roles, and expiration time.
The payload is typically encoded using Base64Url encoding. 


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Token Issuance: 

The server signs the JWT with a secret key using a cryptographic algorithm (e.g., HMAC, RSA, ECDSA).

Token Transmission: 

The server sends the JWT back to the client (usually in an HTTP header, like “Authorization: Bearer  <token>”). 


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The client stores the token for subsequent requests. 

Request Authorization: 

For protected resources, the client includes the JWT in the request header. 

The server verifies the token’s authenticity by recalculating the signature using the stored secret key. If the signature matches and the token is not expired, the request is authorized. 

It’s important to note that JWTs are self-contained and can be decoded by anyone who has the token,  but the signature helps ensure that the token hasn’t been tampered with. Build Modern Web Apps with Mern Stack Course in Pune

Benefits of JWT authentication: 

Stateless: The server doesn’t need to store token information, making it suitable for stateless applications and distributed systems. 

Scalable: The client carries the necessary authentication information, reducing the need for constant database queries. 

Decentralized: Different services can validate JWTs independently if they share the same secret key or have access to the public key. 

However, it’s crucial to properly secure your JWT implementation by following best practices such as using strong cryptographic algorithms, protecting the secret key, setting appropriate expiration times,  and considering token revocation mechanisms. 

Components of a JWT: 


The header typically consists of two parts: the type of the token, which is JWT 

Payload (Claims): 

Claims can be categorized as standard claims (predefined by the JWT specification), public claims  (custom claims defined by you), and private claims (custom claims agreed upon between parties). 

Common standard claims include iss (issuer), sub (subject), aud (audience), exp (expiration time), and iat  (issued at). 

The payload is also base64Url encoded. 


To create the signature part, you have to take the encoded header, encoded payload, a secret key, and  the algorithm specified in the header and sign that. 

The signature is used to verify that the sender of the JWT is who it says it is and to ensure that the  message wasn’t changed along the way. 

Token Flow: 

User Authentication and Token Generation: 

The JWT includes relevant user claims like ID and roles. 

The server signs the JWT with a secret key. 

Token Issuance: 

The client stores the JWT locally, usually in a secure storage mechanism (e.g., localStorage, cookies). Subsequent Requests:

When the client wants to access a protected resource, it includes the JWT in the request header. The server retrieves the JWT from the header and verifies its authenticity using the stored secret key. Token Expiration and Renewal: 

The JWT can include an expiration time claim (exp) to ensure it’s not valid indefinitely. If a token expires, the client needs to obtain a new one by re-authenticating. 


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Benefits and Considerations: 


JWT authentication is stateless, which means the server doesn’t need to maintain session information.  This can improve scalability. 

Cross-Domain Usage: 

JWTs can be used in different domains, making them suitable for single sign-on (SSO) scenarios. Payload Customization: 

JWT payload can be customized with claims to fit specific application requirements. Security Considerations: 

Secret key management is critical. If compromised, the attacker can create and sign their own tokens. Use strong algorithms for signing (e.g., RS256 for RSA or HS256 for HMAC). 

Keep the payload size minimal to reduce overhead. 

Token Revocation: 

JWTs are valid until they expire. To handle immediate revocation (e.g., logout), additional mechanisms are required.

Token Size: 

Since JWTs include both claims and signatures, they can be larger than other authentication methods. 

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Remember that while JWTs are useful for many scenarios, they might not be suitable for all authentication needs. It’s important to evaluate your application’s requirements and security considerations before deciding on JWT authentication.


Pooja Ghodekar

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