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What is OAuth (Open Authorization)?

OAuth is an authorization protocol that grants third-party websites or applications limited access to a user’s information (like their email or photos) — without sharing their logon credentials.

For example, suppose you want to sign up for an app to help you track your fitness goals. Through the power of OAuth, you may have the option to log in using your Google account rather than create a new account specific to the fitness application. In that case, Google will allow the app to access specific data, like your email address and date of birth, without ever sharing your Google password. As a result, the app gets the data it needs to function while your credentials remain secure.

This article explains how OAuth works, provides core best practices for its use, reviews how OAuth differs from other well-known protocols, and offers a solution that complements OAuth to enhance security.

A Brief History of OAuth

OAuth 1.0 development began in 2006 with the goal of enabling individuals to use their OpenID credentials to access other services. However, the protocol proved to be difficult to implement and vulnerable to replay attacks.

OAuth 2.0, released in 2012, provides key improvements, including:

  • Easier implementation because it uses tokens instead of cryptographic signatures
  • More flexibility for different applications because it is designed to support multiple authorization flows, including Authorization Code, Implicit and Client Credentials
  • Extensibility through secure management of API access, enabling developers to build scalable and secure integrations between systems

A new OAuth specification is currently under discussion. The proposed OAuth 2.1 framework consolidates changes made to OAuth 2.0 in the years since its release, with a particular focus on improving security and simplifying implementation.

For now, OAuth 2.0 remains the standard authorization framework. It is used by major companies like Google, Facebook and Microsoft, and it is the version discussed in this document.

The Process of OAuth Explained

Here is a detailed view of the steps in the OAuth 2.0 process:

  1. User requests access: You want to use an app (say, a photo editing app) and choose to log in with your Google account.
  2. User redirected to the authorization server: The application directs you to log in to Google (the authorization server).
  3. User consents: You log in to Google and see a screen asking if you want to allow the application to access certain information (like your photos). You grant permission.
  4. Authorization code issued: Google returns an authorization code to the app.
  5. Application requests token: The app sends this authorization code to Google, along with its client credentials, asking for an access token.
  6. Access token issued: Google verifies the code and sends back an access token.
  7. Resource access: The app uses the token to access your photos from Google (but never sees your Google password).

Core Concepts of OAuth 2.0 Explained

Now, let’s explore the following key OAuth concepts: roles, scopes, authorization codes and access tokens, and grant types.

Roles

OAuth 2.0 defines four main roles:

  • Resource owner — The end-user who owns the data or resource
  • Client — The application that wants to access the resource on behalf of the resource owner
  • Resource server — The server that hosts the protected resources
  • Authorization server — The server that authenticates the resource owner and issues access tokens to the client (such as Google’s OAuth 2.0 server)

Scopes

Scope is a mechanism for limiting an application’s access to a user’s information. The application requests one or more scopes, and the user is asked to consent to sharing of the associated data.

OAuth 2.0 does not define specific values for scopes. Rather, they depend on the native architecture and specific needs of the requesting service. For instance, Google offers a set of scopes so that a user can grant access to their Google Drive but not their Gmail content, or vice versa.

Authorization Codes and Access Tokens

An authorization code is a temporary code that a client app uses to obtain an access token.

This access token is then used to access the information on the resource server that the user has consented to providing, such as their photos or emails.

Grant Types

A grant type is a specific way that a client app can obtain an access token from the authorization server. OAuth 2.0 defines several grant types to accommodate different use cases and security issues. Here are the main ones:

  • Authorization Code — This is the grant type discussed above. Is commonly used by public clients, such as web and mobile apps, to exchange an authorization code for an access token.
  • Resource Owner Password Credentials (PKCE) — With this grant type, The client app directly exchanges the user’s username and password for an access token. Accordingly, it is used when the user trusts the client app with their credentials, as in the case of first-party apps.
  • Client Credentials — Used for machine-to-machine communication where no user is involved, this grant type allows clients to exchange user credentials directly for an access token. Because of the security risks, it is not recommended for modern applications.
  • Device Code — This grant type is designed for devices with limited input capabilities, such as smart TVs or IoT devices. The device displays a code, which the user then enters on another device to authorize the app to receive an access token.
  • Refresh Token —  This grant type enables applications to obtain a new access token without requiring the user to reauthenticate, thereby ensuring uninterrupted access while minimizing user involvement.
  • Implicit — This grant type was previously used by client-side applications (like single-page apps). However, the access token is directly returned without an intermediate authorization code, which increases security vulnerabilities, such as token exposure in browser URLs. Accordingly, this grant type is now largely deprecated.

Best Practices for Securing OAuth Implementations

Securing your OAuth implementation is crucial to protecting user data against unauthorized access. Here are some best practices to follow:

General

  • Always use HTTPS. If tokens are transmitted over an insecure channel, they can be intercepted by attackers. Using HTTPS helps prevent eavesdropping and man-in-the-middle attacks.
  • Always validate redirect URLs. Strictly validate and match redirect URLs to prevent open redirect vulnerabilities, which can be exploited to steal authorization codes or tokens.
  • Implement PKCE. Use Proof Key for Code Exchange (PKCE) to protect against authorization code interception attacks, especially in public clients like mobile apps.
  • Use strong client authentication. Ensure that clients are properly authenticated using strong methods, such as client secrets or mutual TLS.
  • Avoid Implicit grants. With this grant type, the access token is exposed in the URL, making it more susceptible to interception.

Tokens

  • Limit scope of access. Restricting token permissions ensures that applications only access the data they need. Be sure to properly validate the scope of requests.
  • Use short-lived access tokens. Use short-lived access tokens and use Refresh Token grants for longer term access. This approach limits the impact of a compromised token.
  • Store access tokens securely. Tokens should be stored securely to prevent theft and misuse by adversaries.
  • Revoke tokens regularly. Regularly revoke tokens to minimize the risk of token misuse, including replay attacks in which adversaries reuse captured tokens.
  • Implement cross-site request forgery (CSRF) protection. To ensure that requests to the authorization server are legitimate, use anti-CSRF tokens.

Monitoring and Training

  • Monitor and log OAuth activity. Keep detailed logs of OAuth transactions and monitor them for suspicious activity to detect and respond to potential security incidents.
  • Educate users and developers. Provide clear guidance and training on secure OAuth practices for both users and developers. In particular, explain that attackers create fake resource servers to trick clients into sending tokens and how to avoid this type of phishing attack.

OAuth vs. Other Protocols

Swipe left to see the full sheet
ProtocolPrimary purposeKey use cases
OAuth 2.0AuthorizationOAuth is lightweight and user-focused, making it ideal when an app needs to access user data
OpenID Connect (OIDC)Authentication of the user’s identityOIDC is often used in tandem with OAuth: OIDC authenticates users while OAuth provides authorization.
SAMLAuthentication and authorizationSingle sign-on (SSO) for enterprise apps via an XML-based markup language
XACMLPolicy-based access control across systemsEnterprise-wide policy enforcement

How Netwrix Can Help

Implementing OAuth 2.0 can be challenging. Ensuring cross-platform functionality and integrating with legacy systems is technically complex, and careful measures are required to ensure token integrity and security. In addition, organizations need to balance security with a seamless user experience to ensure adoption.

Netwrix simplifies OAuth 2.0 adoption by offering tools and solutions that enhance security, streamline implementation and ensure compliance with best practices. In particular, Netwrix Privilege Secure complements OAuth by managing and securing privileged accounts and access, which are often part of systems leveraging OAuth for authorization. With Netwrix Privilege Secure, you can:

  • Monitor and audit privileged account activity to help ensure that OAuth-based systems are used responsibly.
  • Identify and mitigate security risks related to unauthorized access in OAuth-enabled applications.
  • Secure API credentials and tokens by enforcing least privilege and ensuring proper access controls.

Conclusion

OAuth 2.0 is a cornerstone of modern cybersecurity, enabling secure and flexible authorization for a wide range of applications. With continuous advancements like OAuth 2.1, the framework remains relevant and robust. By following best practices and leveraging tools like those from Netwrix, organizations can maximize the benefits of OAuth 2.0 while minimizing risks. .

FAQs

What is OAuth authentication?

OAuth is a standard open authentication protocol used to grant websites or applications limited access to certain user data on another service without exposing the user’s credentials.

How does OAuth work?

With OAuth, a third-party application can request access to particular user data from another service (the resource server). If the user grants access. the resource server issues an authorization code to the app. The app exchanges this code for an access token, which it uses to request the user’s data from the resource server. This enables the app to access specific data while keeping the user’s credentials private.

What does OAuth provide?

OAuth provides a secure method of granting third-party applications access to user data on another platform without sharing their passwords.

What is OAuth 2?

OAuth 2.0 is an updated version of OAuth. Where OAuth 1.0 uses complex cryptographic methods, OAuth 2.0 uses tokens to grant access. It supports different types of apps, like mobile and web apps, and allows for refreshing tokens without logging in again.

How does OAuth 2 work?

Here is an example the basic OAuth 2.0 workflow:

  1. User requests access: You want to use an app (say, a photo editing app) and choose to log in with your Google account.
  2. User redirected to the authorization server: The application directs you to log in to Google (the authorization server).
  3. User consents: You log in to Google and see a screen asking if you want to allow the application to access certain information (like your photos). You grant permission.
  4. Authorization code issued: Google returns an authorization code to the app.
  5. Application requests token: The app sends this authorization code to Google, along with its client credentials, asking for an access token.
  6. Access token issued: Google verifies the code and sends back an access token.
  7. Resource access: The app uses the token to access your photos from Google (but never sees your Google password).

David, a Solutions Engineer at Netwrix, brings over 25 years of IT experience and certifications as a Microsoft and VMware trainer. He has trained hundreds of IT professionals across industries, gaining deep insight into the security and compliance challenges organizations face. At Netwrix, David leverages his technical expertise and customer-focused approach to help clients strengthen their cybersecurity, mitigate risks, and meet regulatory requirements.