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Redirect Users With State Parameters

You can store the application state parameter before you redirect users to authenticate so that you can redirect them back to a URL. For example, if a user intends to access a protected page in your application, and that action triggers the request to authenticate, you can store that URL to redirect the user back to their intended page after the authentication finishes.

Use the state parameter to lookup and restore the previous state of your application. Generate and store a nonce locally (cookies/session/localstorage), along with any desired state data (like the redirect URL). Use the nonce as a state in the protocol message. If the returned state matches the stored nonce, accept the OAuth2 message and fetch the corresponding state data from storage. This is the approach used by Auth0.js.

  1. Generate the nonce that you will use to protect against CSRF attacks as explained before. Store the nonce locally, using it as the key to store all the other application state like the URL where the user intended to go. For example:

    {
      "xyzABC123" : {
        redirectUrl: '/protectedResource',
        expiresOn: [...]
      }
    }
    
  2. Authenticate the user, sending the generated nonce as the state.

  3. As part of the callback processing and response validation, verify that the state returned matches the nonce stored locally. If it does, retrieve the rest of the application state (like the redirectUrl).

  4. Once you complete the callback processing, redirect the user to the URL previously stored.

    Again, how you store the nonce and the URL or other information pertinent to the application state depends on your application's type. It can be local storage in single-page or native apps or a cookie in a regular web app.

Alternate method

Alternatively, you can:

  1. Generate and store a nonce locally.

  2. Encode any desired state (like the redirect URL) along with the nonce in a protected message (that will need to be encrypted/signed to avoid tampering).

  3. In the response processing, unprotect the message, getting the nonce and other properties stored.

  4. Validate that the included nonce matches what was stored locally and, if so, accept the OAuth2 message.

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