Why are JWTs used in API security?

Structure

JWTs are a means of securely transmitting information as a JSON object over a network. JWTs also come with a time limit. Once this limit expires, they’ll be rendered invalid, and a new token has to be generated (through refresh tokens).

JWTs consist of three parts:

1. Header: Defines the token’s type and the algorithm used to sign it

2. Payload: Contains claims and information about the entity the token is assigned to.

3. Signature: Verifies the legitimacy of the token.

An example of a JWT structure is shown below:

Note: The three parts are seperated by ..

Authentication

APIs widely employ the use of JWT for authentication purposes. An illustration depicting this process is provided below:

The process involves a client sending their credentials to an authentication endpoint (at the server). Upon verification, the server generates a JWT, which is returned to the client. The client stores the JWT and includes it in further requests as an authorization mechanism. Through this JWT, the server authenticates the client and any requests it makes.

Authorization

Apart from authentication, JWTs can also be utilized for authorization purposes. This involves using the payload of a JWT. These claims contained inside the payload can be used to provide the information for determining what actions and op the client is authorized to perform. The server can restrict access to certain API endpoints or resources by evaluating a client’s payload.

Benefits

The advantages of using JWTs for API security are mentioned as follows:

• Compatibility: JWTs are utilized across different platforms, allowing for seamless integration in third-party applications.

• Enhanced security: The signature within a JWT ensures its integrity and prevents tampering.

• Flexibility: The payload of a JWT can contain custom claims (application-specific information) for authorization purposes.

• Stateless: Servers don’t need to maintain session information for JWTs are they’re stateless. Because the token is not stored, it reduces the risk of session-related attacks.

• Scalable: Being stateless also makes JWTs highly scalable, as the server can process requests without needing server-side sessions.

Best practices

To maximize the security and effectiveness of JWTs, it is essential to follow these best practices:

1. Use strong cryptographic algorithms (HMAC-SHA256/RSA) for signing JWTs.

2. We should assign expiration times for JWTs to balance their security and usability. Shorter expiration times reduce the chances of the token being compromised. Longer times reduce the need for token regeneration.

3. Maintain token blocklists to invalidate compromised/expired tokens.

4. Use TLSTransport Layer Security, which prevents token interception.