OAuth 2 Refresh Tokens: A Practical Guide

What Is an OAuth 2 refresh token? 

An OAuth 2 refresh token is a credential used to obtain a new access token without re-authenticating the user. It allows applications to access protected resources without prompting for credentials again. This is useful when access tokens have a short lifespan.

Refresh tokens are issued alongside access tokens during the authentication process. Once the access token expires, the refresh token can be sent to the authorization server to obtain a new access token. This mechanism improves security by minimizing the time an access token is valid, reducing the impact of a compromised token.

Understanding tokens in OAuth 2

Tokens in OAuth 2 represent a user’s permission to access certain resources on a server. OAuth 2 primarily uses two types of tokens: access tokens and refresh tokens. Access tokens allow resource access for a limited duration, while refresh tokens are used to generate new access tokens.

The token system is central to OAuth 2’s scalability and security. By decoupling user authentication and resource access, OAuth reduces the need to frequently prompt users for authentication. These tokens should be short-lived to mitigate security risks associated with token theft or misuse.

Access tokens vs refresh tokens

Access tokens bear the user’s authorized scope of access and typically expire quickly to limit misuse risk. Applications must replace expired access tokens by re-authenticating users or using refresh tokens if available.

Refresh tokens are long-lived and can be used to obtain new access tokens without further user interaction. This mechanism trades off user convenience with the ability to maintain sessions across extended periods.

Token lifetimes and expiration

Token lifetimes aid in maintaining the balance between security and user convenience in OAuth 2. Access tokens should have short expiration times, such as minutes or hours but can vary greatly, to minimize the potential damage in case of compromise. Frequent expiration and renewal of access tokens help contain any security risks promptly.

Refresh tokens typically have longer expirations, often lasting days or weeks. They provide a measure of persistent access while still ensuring security through periodic access token renewal. Applications use the refresh token to obtain new access tokens after the current one expires, maintaining uninterrupted service access while controlling token lifespan.

How refresh tokens work 

When initially authenticating, an access token and a refresh token are generated. When the access token expires, the refresh token is sent to the authorization server, which validates it before issuing a new access token. Refresh tokens follow the refresh token grant flow in OAuth 2.0. 

The refresh token grant flow

In this flow, a valid refresh token is exchanged with the authorization server for a new access token. The client sends the refresh token along with its credentials to authenticate the request. If validated, the server issues a fresh access token that extends the client’s access to the user’s protected resources access.

This grant flow improves user experience by limiting the frequency of authentication prompts. It allows applications to access protected resources without disruptive user interactions when access tokens expire.

Request and response parameters

In the refresh token grant flow, parameters include the grant_type set to refresh_token, the actual refresh token, and client authentication credentials. Depending on the authorization server, additional parameters may be required.

Upon successful validation, the response from the server includes a new access token. Optional parameters might also specify token type, typically bearer, and scope, indicating the permissions the application has requested on behalf of the user.

When to use refresh tokens 

Refresh tokens are useful when users need to have access for a long period of time, but it is undesirable for the user to repeatedly authenticate. They are typically used in applications with persistent login experiences, such as mobile apps, web platforms, and APIs that require extended user interaction.

Refresh tokens are most beneficial when:

• Access tokens have short expiry times: If the access tokens have a short lifespan (e.g., a few minutes or hours depending on the use case), refresh tokens can help avoid frequent user re-authentication by providing new access tokens.
• User experience is a priority: In applications where uninterrupted access is essential (e.g., background services), refresh tokens allow the system to maintain user sessions without disrupting workflows.By limiting the need for users to re-enter credentials, refresh tokens provide a balance between security (short-lived access tokens) and convenience (automatic renewal via refresh tokens).

However, refresh tokens are not always necessary. For one-time access, short-lived sessions, or highly secure environments where token lifetimes are tightly controlled, refresh tokens may be omitted to reduce the potential attack surface.

Security considerations with refresh tokens 

Because of their use for long-term user sessions, refresh tokens present attractive targets for attackers. This makes it crucial for developers to ensure that they are stored securely, inaccessible to unauthorized parties. 

Storing refresh tokens securely

Storing refresh tokens in secure, encrypted storage helps protect them. Developers should avoid storing these tokens in insecure locations like browser localStorage, favoring secure server-side storage or secure client-device storage solutions. 

Using encrypted and isolated storage mechanisms ensures tokens remain protected. Applications must also incorporate stringent access controls for stored tokens. This helps ensure that only authorized components can access these tokens via secure APIs.

Token revocation strategies

Token revocation helps ensure that compromised or expired tokens cannot be misused. This strategy involves invalidating refresh tokens when certain triggers occur, such as user logout, suspicious activity detection, or after a specified time interval. Immediate revocation prevents unauthorized access, minimizing potential damage from compromised tokens.

Effective revocation strategies also ensure comprehensive logging and monitoring mechanisms are in place. By tracking token usage patterns and implementing anomaly detection, systems can identify and revoke suspicious tokens.

Refresh token rotation and reuse detection

Refresh token rotation improves security by issuing a new refresh token each time an access token is refreshed. With rotation, a compromised refresh token becomes invalid after use, reducing the risk of repeated unauthorized access. This process ensures that even if a refresh token is intercepted, misuse opportunities are limited and easily detectable.

Implementing reuse detection further strengthens security by monitoring for multiple uses of the same refresh token. If a token is reused, it signals a potential compromise, triggering safeguards like token invalidation or user re-authentication.

Best practices for using refresh tokens 

Implementing the following best practices for refresh tokens can help improve both application security and the user experience. 

Use short-lived access tokens

Short-lived access tokens limit the window of opportunity for misuse if compromised. These tokens have lifetimes that force frequent renewals, ensuring that applications check for valid user sessions at regular intervals.

The combination of short-lived access tokens with refresh tokens reduces user friction. As tokens expire, refresh tokens issue new access tokens, preventing service disruption while maintaining a secure environment.

Secure client authentication

Strong client authentication protocols, including multi-factor authentication (MFA), improve security by verifying both user identity and request authenticity. By ensuring that only verified clients can use refresh tokens, unauthorized token refresh requests are blocked.

Access controls should be strict, with well-defined scopes and permissions for each client. Encrypting token transmission and implementing secure communication protocols further ensures that refresh tokens are handled safely.

Implement refresh token rotation

Refresh token rotation adds a security layer by ensuring each token is single-use. As tokens are used to obtain new access tokens, they are replaced with new refresh tokens, mitigating reuse risks if tokens are intercepted.

Rotation also aids in detecting suspicious activity, as repeated use of the same refresh token indicates a breach. This automated protection mechanism supports security practices, demanding minimal user intervention while ensuring tokens are continually refreshed.

Monitor for suspicious activity

Continuous monitoring for suspicious activity is critical in managing refresh tokens. By tracking token usage patterns, systems can identify anomalies such as repeated authentication failures or unusual access requests, leading to proactive security interventions.

When continuous monitoring is in place, it is possible to trigger token invalidation or user notifications when unusual activity is detected. This can help security teams identify and prevent unauthorized access. Monitoring processes must be integrated into an overall security strategy, providing real-time insight and response to threats.

Revoke tokens when necessary

Revoking tokens is essential in maintaining the security of OAuth implementations. Tokens should be revoked promptly on detecting compromise, such as unusual access patterns or after logout events. Immediate revocation prevents further unauthorized use.

Implement stringent mechanisms to revoke refresh tokens through administrative controls or automated systems. Systems must handle revocation gracefully, ensuring users are re-authenticated seamlessly when necessary.

Using OAuth with Frontegg

Frontegg provides an end-to-end authentication platform that eliminates developer bottlenecks and empowers non-technical stakeholders. Built on JSON Web Tokens (JWTs) that adhere to the highest security standards, our solution ensures seamless compliance with OAuth protocols and OpenID Connect 1.0 (OIDC).

By leveraging Frontegg, developers can spend less time managing identity tasks, while non-technical teams gain the tools to handle essential aspects of authentication and authorization independently. This distributed ownership model means faster decision-making, enhanced security, and a better experience for everyone in the SaaS ecosystem. 

Whether you’re scaling a startup or managing a complex multi-tenant SaaS, Frontegg’s low-code capabilities make integration swift and painless, allowing your team to focus on what matters most—building your product.

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