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OAuth 2 is an open standard protocol that allows users to share their private resources stored on one site with another site without having to provide their credentials. Essentially, OAuth 2 provides secure delegated access to server resources on behalf of the resource owner. It specifies a process for resource owners to authorize third-party access to their server resources.
OAuth 2 provides an authorization framework that allows applications to obtain limited access to user accounts on an HTTP service. It works by delegating user authentication to the service that hosts the user account, and authorizing third-party applications to access the user account. OAuth 2 provides several ‘grant types’ for different use cases, each of which is really a different method of obtaining authorization.
Developed by the IETF OAuth Working Group, OAuth 2 is not backwards compatible with OAuth 1.0. This is because OAuth 2 focuses on client developer simplicity while providing specific authorization flows for web applications, desktop applications, mobile phones, and living room devices.
In this article:
Key benefits of OAuth 2 include:
Learn more in our detailed guide to OAuth flow
Comparing OAuth 1 and OAuth 2, there are several key differences to note. OAuth 1 was the first version of OAuth and it was quite complex. It required the use of cryptographic libraries for signature generation and verification, which made it difficult to develop and debug.
On the other hand, OAuth 2 is much simpler and easier to use. It does not require cryptography on the client side, which makes it much simpler to work with. OAuth 2 also provides a variety of “grant types” to cover different use cases, making it more flexible and versatile.
However, it’s important to note that OAuth 2 is not backwards compatible with OAuth 1. This means that applications using OAuth 1 need to be updated to use OAuth 2, which can be a significant task.
Learn more in our detailed guide to OAuth grant types
The OAuth 2.0 protocol flow involves several steps. First, the client (the application requesting access) sends a request to the resource owner (the user) to authorize access. This request is sent to the authorization server, which presents the request to the resource owner and obtains authorization consent.
Once the authorization server receives the consent, it issues an authorization grant to the client. The client then presents this authorization grant to the authorization server and requests an access token. The authorization server authenticates the client and validates the authorization grant. If valid, it issues an access token to the client.
The client can now use this access token to access the protected resources hosted by the resource server. The resource server validates the access token, and if valid, serves the requested resources to the client. It’s important to note that throughout this process, the client never sees the resource owner’s credentials.
When implementing OAuth 2, it is important to use secure communication for all interactions between the client, authorization server, and resource server. To achieve this, you should always use HTTPS (Hypertext Transfer Protocol Secure) for all communications. HTTPS encrypts the data sent between the client and server, ensuring that it cannot be read or modified while in transit.
Using secure communication is not only a best practice for OAuth 2 implementation, but it is also a requirement. The OAuth 2 specification clearly states that all communication must be secured using TLS (Transport Layer Security) or a similar secure transport mechanism. This is to prevent attacks such as eavesdropping, man-in-the-middle attacks, and request forgery, which can compromise the security of the OAuth 2 process.
Furthermore, the access tokens issued by the authorization server in OAuth 2 are bearer tokens. This means that anyone who gets hold of the token can use it to access the protected resources. Therefore, if these tokens are intercepted during transmission, an attacker could gain unauthorized access to the resources. Hence, the importance of secure communication cannot be overstated.
In OAuth 2, using PKCE (Proof Key for Code Exchange) is a best practice for mobile and native applications. PKCE is a security extension to OAuth 2 and it helps to prevent a class of attacks known as authorization code interception (ACI) attacks. These attacks occur when an attacker intercepts the authorization code as it is being transmitted from the authorization server to the client.
Here is a quick overview of how PKCE works:
OAuth 2 provides several grant types, each designed for different client types and use cases. When implementing OAuth 2, it is crucial to choose the right grant type for your application. The grant type determines the steps taken by the client to obtain an access token and should be chosen based on the capabilities and requirements of the client application.
For web applications, the authorization code grant type is typically the best choice. This grant type is used when the client is a web server, and it can securely store the client secret and interact with the user’s web browser. The Authorization Code grant type provides a high level of security, as the access token is never exposed to the user’s web browser.
For mobile or native applications, the Implicit grant type or the authorization code with PKCE (Proof Key for Code Exchange) is recommended. The Implicit grant type is used when the client is a user-agent-based application (like a single-page web app) that can’t securely store the client secret. In this case, the access token is returned directly to the user-agent without an intermediate code exchange step.
Access tokens in OAuth 2 should have a limited lifetime. This means they should expire after a certain period of inactivity. When a token expires, the client must obtain a new one by either using a refresh token or initiating a new authorization request.
Implementing token revocation is also important. This allows the resource owner (the user) or the authorization server to invalidate a token before it expires. If a token is revoked, any future requests using that token should be denied. This is particularly useful in situations where a token may have been compromised, or when the user wants to deauthorize a client application.
In OAuth 2, the redirect URI is the location where the authorization server sends the user after granting or denying their authorization request. It’s crucial to ensure the security of the redirect URI as it’s a common target for attackers. An attacker could manipulate the redirect URI to trick the user into authorizing access to their resources, or to steal the authorization code or access token.
To secure the redirect URI, always use absolute URIs and avoid using wildcard or open redirectors. Also, ensure that the authorization server only sends the authorization response to pre-registered and validated redirect URIs. This way, even if an attacker manages to manipulate the redirect URI in the authorization request, the server will not send the response to an unregistered or unvalidated URI.
OAuth 2 does not handle user sessions, but it’s important to implement proper session management in your application alongside OAuth 2. A session is a period of interaction between a user and an application. When a user logs into an application, a session is created, and when they log out, the session is destroyed.
Session management helps to identify and manage the user’s state and interaction with the application while they’re logged in. It’s crucial to ensure the security of the user’s session, as an attacker who gains access to a user’s session could impersonate the user and gain unauthorized access to their resources.
To implement proper session management, always use secure and httpOnly cookies to store session identifiers, and implement idle and absolute timeouts for sessions. Also, regenerate the session identifier after login and during significant events to prevent session fixation attacks.
In OAuth 2, scopes are used to specify the permissions that an access token grants. Scopes are included in the authorization request and are displayed to the user during the consent process. The user can then decide what permissions to grant to the client application.
Utilizing token scopes allows you to limit the level of access that an access token grants. For instance, you could issue an access token that only allows read access to a user’s resources, or one that allows both read and write access. This way, even if an access token is compromised, the attacker’s actions would be limited by the scope of the token.
Furthermore, using scopes allows the user to have more control over what resources a client application can access. During the consent process, the user can see what permissions the client is requesting and decide whether to grant or deny these permissions. This contributes to a more transparent and user-friendly OAuth 2 process.
Looking ahead, the future of OAuth is OAuth 2.1. This new version aims to simplify the OAuth 2 protocol by removing some lesser-used and difficult to understand features. It also aims to improve security by making some of the recommended best practices mandatory.
OAuth 2.1 includes several changes, such as removing the implicit and password grant types, requiring explicit user consent for authorization, and requiring PKCE (Proof Key for Code Exchange) for all OAuth 2.1 clients.
Frontegg’s end-to-end and self-served authentication infrastructure is based on JSON Web Tokens. Our JWTs have been designed to adhere to the highest security standards. Therefore, our user management solution is also fully compliant with the OAuth protocol, along with OpenID Connect 1.0 (OIDC) as well. We cover all important bases that are required in the modern SaaS space.
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