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What is JWT?

At its core, JWT is just a JSON object that is efficiently encoded as a string. However, encoded strings can be easily manipulated, so JWT also includes a signature that allows you to verify that the string has not been tampered with.

In the context of authentication, signed JWTs are used to represent authenticated user sessions. When a user logs in, a signed JWT is created and sent to the user’s browser. The signed JWT includes the user’s session information, such as the user’s ID, email, and other properties - but most importantly, it includes the server’s cryptographic signature and an expiration time. This JWT is then sent back to the server with subsequent requests, allowing the server to verify that the user is authenticated.

Because the JWT exists only on the client side, and is verified by the server, it has advantages and disadvantages:

  • It can be used without cookies (for example, using the bearer authentication scheme for REST APIs)
  • The server can verify the JWT without having to maintain a session on the server side or making database calls.
  • It is easily manipulated, so it is important to verify the signature and check the expiration time.
  • It cannot be revoked once issued, an issued JWT will remain valid until it expires.

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JWT Usage in Nile Auth

Nile Auth uses JWTs to represent user sessions for the email + password provider. For other providers, database sessions are used instead.

You never need to deal with JWTs directly - Nile Auth and Nile SDK are responsible for creating, verifying and storing them. You can access the current JWT using the useSession hook (client side), or by calling nile.api.auth.getSession (server side).

You can learn more about sessions in the Sessions documentation - which includes information about working with user sessions whether they are represented by JWTs or database sessions.

However, it is useful to understand how JWTs work and what they contain.

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JWT Structure

The JWT used by Nile Auth contains the ID of the user (sub - the subject that the token refers to), the user’s email, and the expiration time.

{
  "sub": "1234567890",
  "email": "test@example.com",
  "exp": 1715027200
}

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Security Considerations

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Token Storage

Tokens should be stored securely on the client side - this typically means using secure, httpOnly cookies. Storing tokens in local storage or session storage is not recommended, as this makes them susceptible to XSS attacks.

Nile Auth uses secure, httpOnly cookies by default. So you typically don’t need to worry about this.

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Token Expiration

Nile Auth sessions expiration time is set to 30 days, and this applies to both database sessions and JWT sessions. Because JWT sessions are stateless, they cannot be revoked once issued. However, you can remove the user from specific tenants and disable their access to them.

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Best Practices

When working with JWTs, there are several important security practices to follow. Nile Auth implements all of these best practices by default:

  • Use Strong Signatures: Always use strong cryptographic algorithms (like RS256) for signing JWTs. Never use weak algorithms or “none”.
  • Keep Tokens Small: JWTs should contain only essential claims to minimize token size and reduce overhead.
  • Secure Token Transmission: Always transmit tokens over HTTPS and use secure, httpOnly cookies.
  • Validate All Claims: Always verify the signature and validate all claims (especially expiration) before trusting a token.
  • Don’t Store Sensitive Data: Avoid storing sensitive information in JWTs as they are stored on the client side and are only signed, not encrypted.

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