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What is OAuth

  • What is OAuth? OAuth is an open-standard authorization protocol or framework that describes how unrelated servers and services can safely allow authenticated access to their assets without actually sharing the initial, related, single logon credential. In authentication parlance, this is known as secure, third-party, user-agent, delegated authorization.

  • Give an example of what using OAuth would look like. The simplest example of OAuth is when you go to log onto a website and it offers one or more opportunities to log on using another website’s/service’s logon. You then click on the button linked to the other website, the other website authenticates you, and the website you were originally connecting to logs you on itself afterward using permission gained from the second website.

  • How does OAuth work? What are the steps that it takes to authenticate the user? OAuth allows websites and services to share assets among users. It is widely accepted, but be aware of its vulnerabilities.

  • What is OpenID? There are a couple of other security technologies that you might hear about in the same context as OAuth, and one of them is OpenID. At a base level, the distinction between the two is simple to grasp. Remember when we said up above that the auth in OAuth stood for authorization, not authentication? Well, OpenID is about authentication: as a commenter on StackOverflow pithily put it: “OpenID is for humans logging into machines, OAuth is for machines logging into machines on behalf of humans.”

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Authorization and Authentication flows

  • What is the difference between authorization and authentication? Auth0 uses the OpenID Connect (OIDC) Protocol and OAuth 2.0 Authorization Framework to authenticate users and get their authorization to access protected resources. With Auth0, you can easily support different flows in your own applications and APIs without worrying about OIDC/OAuth 2.0 specifications or other technical aspects of authentication and authorization.

  • What is Authorization Code Flow? Because regular web apps are server-side apps where the source code is not publicly exposed, they can use the Authorization Code Flow (defined in OAuth 2.0 RFC 6749, section 4.1), which exchanges an Authorization Code for a token. Your app must be server-side because during this exchange, you must also pass along your application’s Client Secret, which must always be kept secure, and you will have to store it in your client.

  • What is Authorization Code Flow with Proof Key for Code Exchange (PKCE)? During authentication, mobile and native applications can use the Authorization Code Flow, but they require additional security. Additionally, single-page apps have special challenges. To mitigate these, OAuth 2.0 provides a version of the Authorization Code Flow which makes use of a Proof Key for Code Exchange (PKCE).

  • What is Implicit Flow with Form Post? As an alternative to the Authorization Code Flow, OAuth 2.0 provides the Implicit Flow, which is intended for Public Clients, or applications which are unable to securely store Client Secrets. While this is no longer considered a best practice for requesting Access Tokens, when used with Form Post response mode, it does offer a streamlined workflow if the application needs only an ID token to perform user authentication.

  • What is Client Credentials Flow? With machine-to-machine (M2M) applications, such as CLIs, daemons, or services running on your back-end, the system authenticates and authorizes the app rather than a user. For this scenario, typical authentication schemes like username + password or social logins don’t make sense. Instead, M2M apps use the Client Credentials Flow (defined in OAuth 2.0 RFC 6749, section 4.4).

  • What is Device Authorization Flow? With input-constrained devices that connect to the internet, rather than authenticate the user directly, the device asks the user to go to a link on their computer or smartphone and authorize the device. This avoids a poor user experience for devices that do not have an easy way to enter text. To do this, device apps use the Device Authorization Flow (drafted in OAuth 2.0). For use with mobile/native applications.

  • What is Resource Owner Password Flow? Though we do not recommend it, highly-trusted applications can use the Resource Owner Password Flow, which requests that users provide credentials (username and password), typically using an interactive form. The Resource Owner Password Flow should only be used when redirect-based flows (like the Authorization Code Flow) cannot be used.

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