Protecting your APIs with OAuth: Security and Strenght of Access Tokens.
OAuth stands for Open Authorization.
It is an open standard protocol for secure, delegated access to web services and resources, enabling third-party applications to access user data without revealing credentials. OAuth enables single sign-on (SSO) solutions, enabling users to access multiple services using trusted identities like (Facebook or Google) providers without sharing credentials individually. It is widely adopted in web services and APIs.
OAuth is widely used in social media login, API access, and other secure, delegated access scenarios without sharing sensitive credentials. With several versions, OAuth 2.0 is the most widely adopted. It focuses on authorization and access delegation, often using OpenID Connect for user authentication.
OAuth ensures user data and resource protection through secure access tokens, relying on implementation and management by authorization and resource servers.
Here's how OAuth works at a high level:
Looking at the following roles;
Resource Owner: The user owns data or resources for third-party applications to access, while the client is the third-party application attempting to access them.
Client: The client is the third-party application or service that wants to access the user's resources. For example, a mobile app that wants to post photos to the user's social media account.
Authorization Server: The authorization server authenticates the user and obtains consent, issues access tokens, and stores user data or resources. It issues access tokens to authorized clients.
Resource Server: The resource server verifies the access token provided by the client to ensure permission. It has permission to access the requested resources.
Authorization Request: The authorization request involves the client requesting permission to access resources on behalf of the user. Requesting permission to access specific resources on behalf of the user.
User Authentication and Consent: The authorization server authenticates the user, issues an authorization grant, and sends a token in exchange. The authorization server validates the grant and issues an access token, which the client uses to access protected resources.
Authorization Grant: The authorization server issues an authorization grant (an access code) to the client with the user consent.
Token Request: The client sends the authorization grant to the authorization server in exchange for an access token.
Access Token: The authorization server validates the authorization grant and issues an access token to the client.
Resources Access: The client uses the access token to access the protected resources on the resources server. The resource server validates the token and if it’s valid, grants access to the requested resources.
Security and Strength of Access Tokens.
OAuth itself provides a framework for authentication and authorization, the strength of the tokens often depends on how they are implemented and managed by the authorization server and the resource server.
Considerations for ensuring strong OAuth tokens:
Token Length and Complexity: Ensure access tokens are sufficiently long and complicated. It is more difficult to guess or use brute force on longer tokens containing a mixture of characters (letters, numerals, and symbols). For token length, 128 bits (16 bytes) is the minimum acceptable value.
Token Entropy: Tokens must be produced using cryptographically safe random number generators to have a high entropy. An attacker would have a very tough time predicting or guessing valid tokens due to this randomness.
Rotate tokens: Put policies in place for rotating tokens. Use short-lived access tokens and routine access token refreshes to reduce the window of opportunity for attackers if a token is compromised.
Token Scope: Tokens should only be used to access the precise resources and actions that the client application requires. Keep away from showing too much leniency.
Transport Layer Security (TLS): To avoid eavesdropping and man-in-the-middle attacks, make sure that token transmission between the client, authorization server, and resource server is secured by TLS (Transport Layer Security).
Storage of Tokens: Both the resource server and the client should securely store tokens. Use secure storage systems on the client side, such as the Android Keystore or the iOS Keychain. Keep tokens that have been salted and hashed on the server side.
Token Revocation: Provide procedures for token revocation so that users can deny access to their data if they believe their token has been compromised. A standard for token revocation is provided by OAuth (RFC 7009).
Audience and Issuer Validation: To guarantee that the token was issued by the anticipated authorization server and was meant for the specific client, both the client and the resource server need to verify the audience (aud) and issuer (iss) assertions in the token.
Rate Limiting and Monitoring: Add rate limits on token requests to stop brute force attacks. Rate monitoring is also essential. Keep an eye out for any strange or suspicious conduct when using tokens.
Consider encrypting the contents of tokens, especially if they contain sensitive data. Even if the tokens are somehow intercepted, this gives an additional layer of protection.
Token Signing: Employ digital signatures when signing tokens so that the resource server can confirm the legitimacy of the token issuer. For signed tokens, the JSON Web Token (JWT) format is frequently used.
To learn more about OAuth start with these courses;
Getting started with OAuth 2.0 by Pluralsight.
Video Course: The Nuts and Bolts of OAuth 2.0
Getting Started OAuth Simplified