What is an Authentication token?

An authentication token is a cryptographically signed string that encapsulates claims—statements that convey information about the user, such as their identity, roles, or permissions. 

Tokens verify identity without requiring an active session on the server, providing a secure and flexible way to manage access control for your application’s resources and APIs.

Applications often store tokens in secure HTTP-only cookies to prevent unauthorized access and client-side attacks like XSS. Tokens typically expire after a set time or when a user logs out, minimizing the risk of misuse.

In this article, we’ll cover authentication tokens, the different types, and how to generate and secure them.

How do authentication tokens work?

When a user logs into an application, they prove their identity by providing credentials, such as a password or a second factor, like a one-time passcode. Once verified, the application or identity provider generates an authentication token representing the user’s identity and permissions.

This token is then securely stored on the user’s device, typically in an HTTP-only cookie, which is protected against client-side attacks. Note that while HTTP-only cookies are safer against XSS, they require CSRF protection measures. In contrast, storing tokens in local storage is more prone to XSS attacks and is generally recommended only for short-lived, non-sensitive tokens.

With each user request, the token is sent in an HTTP header or cookie, allowing the server to verify the user’s identity and permissions without needing a server-side session. The application checks the token’s validity with each request. If valid, the user continues to have access; otherwise, they are prompted to re-authenticate for a new token.

Types of authentication tokens

The main types of authentication tokens include:

• Access Tokens: Short-term tokens for limited access, typically used in API requests to minimize security risks.

• Refresh Tokens: These longer-lived tokens are used to obtain new access tokens without re-authentication and are stored securely to prevent misuse.

• JSON Web Tokens (JWTs): JWTs are self-contained tokens that encode user information and claims in JSON format, signed with a secret or private key to prevent tampering. They are commonly used for stateless authentication.

These token types are customizable to meet varying security needs, with expiration times, scopes, and permissions tailored to the application’s requirements.

Why use authentication tokens?

Authentication tokens offer several benefits for secure, efficient user access management:

• Single Sign-On (SSO): Tokens enable SSO, allowing users to log in once and gain access to multiple apps without needing to re-authenticate. Protocols like OpenID Connect (OIDC) use tokens with user information to manage service access.

• Temporary Access: Tokens can be configured with expiration times, ideal for managing sessions that expire after inactivity or for temporary access to APIs or restricted areas.

• Granular Access Control: Tokens include claims specifying user roles and permissions, allowing applications to enforce Role-Based Access Control (RBAC) or fine-grained permissions directly from token data.

• Enhanced Security: Tokens improve security through signatures for data integrity, support for multi-factor authentication (MFA), and short expiration times that limit token exposure.

• Microservices Authentication: In microservices architectures, stateless tokens let services authenticate requests independently without complex inter-service communication.

• Improved User Experience: Tokens allow users to stay logged in without re-entering credentials, streamlining access to various parts of the application.

Authentication tokens vs. JWTs

JSON Web Tokens (JWTs) are a popular type of authentication token. They are compact, URL-safe, and self-contained. JWTs are useful for stateless authentication, as they carry user information within the token, eliminating the need for server-side sessions.

A JWT is composed of three distinct parts, each Base64 URL-encoded and separated by dots (.) to form the final token:

1. Header: Contains metadata specifying the token type (JWT) and the signing algorithm (e.g., HS256 for HMAC SHA-256 or RS256 for RSA SHA-256).

{
  "alg": "HS256",
  "typ": "JWT"
}

2. Payload (Claims): Contains claims with user-specific information like ID, roles, or permissions. Example:

{
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022,
  "exp": 1516242622,
  "roles": ["user", "admin"]
}

3. Signature: Verifies the token’s integrity by signing the Base64-encoded header and payload, separated by a dot (.), using the specified algorithm and a secret or private key.

The final JWT structure is <header>.<payload>.<signature>, allowing secure, stateless user authentication across distributed applications and microservices.

How to generate and secure authentication tokens

Here’s a typical process for generating a JWT:

1. Define the Header: Specify the token type (JWT) and the signing algorithm (e.g., HS256 or RS256). For example:

{
  "alg": "RS256",
  "typ": "JWT"
}

2. Define the Payload: The payload contains claims about the user. Use registered claims (e.g., sub for subject, exp for expiration) and any custom claims (e.g., user roles) needed by the application. Example:

{
  "sub": "1234567890",
  "admin": true,
  "iat": 1516239022,
  "exp": 1516239922
}

3. Create the Signature: Concatenate the Base64-encoded header and payload with a dot (.) and sign this data using the specified algorithm and a private key (for RS256).

4. Combine to Form the JWT: Concatenate the encoded header, payload, and signature into a single string separated by dots (.), forming the JWT.

Most applications use libraries like jsonwebtoken (Node.js), pyjwt (Python), or ruby-jwt (Ruby) to generate and manage JWTs.

Authentication token best practices

To maximize the security and effectiveness of authentication tokens, follow these best practices:

• Use HTTPS: Always use HTTPS to transmit tokens, reducing the risk of interception.
• Set Expiration Times: Configure short expiration times for access tokens, particularly for sensitive applications. This reduces the risk of token theft and replay attacks.
• Store Tokens Securely: For web applications, use HTTP-only cookies to store tokens. Avoid local storage for long-lived tokens to reduce exposure to XSS attacks.
• Avoid Sensitive Data in Tokens: Do not include sensitive information (like passwords or personal data) in tokens. If sensitive data must be included, encrypt the token.
• Implement Token Revocation: Use a token revocation list or blacklist to invalidate tokens that are compromised or no longer valid.‍
• Rotate Keys: Regularly rotate signing keys for tokens to maintain a high level of security and reduce the risk of unauthorized access.

How to implement SSO quickly and easily

WorkOS offers a streamlined, API-based way to support enterprise SSO in your app. 

By connecting with major identity providers like Okta and Microsoft Entra, WorkOS simplifies integration with comprehensive SDKs, clear documentation, and dedicated support.

‍Sign up for WorkOS today, and start selling to enterprise customers tomorrow.