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Send SSO attributes to Access-protected origins with Workers

Last reviewed: 6 days ago

This tutorial will walk you through extending the single-sign-on (SSO) capabilities of Cloudflare Access with our serverless computing platform, Cloudflare Workers. Specifically, this guide will demonstrate how to modify requests sent to your secured origin to include additional information from the Cloudflare Access authentication event.

Time to complete: 45 minutes

Authentication flow

Cloudflare Access is an authentication proxy in charge of validating a user’s identity before they connect to your application. As shown in the diagram below, Access inserts a JWT into the request, which can then be verified by the origin server.

Standard authentication flow for a request to an Access application

You can extend this functionality by using a Cloudflare Worker to insert additional HTTP headers into the request. In this example, we will add the device posture attributes firewall_activated and disk_encrypted, but you can include any attributes that Cloudflare Access collects from the authentication event.

Extended authentication flow uses a Worker to pass additional request headers to the origin

Benefits

This approach allows you to:

  • Enhance security: By incorporating additional information from the authentication event, you can implement more robust security measures. For example, you can use device posture data to enforce access based on device compliance.
  • Improve user experience: You can personalize the user experience by tailoring content or functionality based on user attributes. For example, you can display different content based on the user’s role or location.
  • Simplify development: By using Cloudflare Workers, you can easily extend your Cloudflare Access configuration without modifying your origin application code.

Before you begin

1. Create the Worker

  1. Create a new Workers project:

    Terminal window
    npm create cloudflare@latest -- device-posture-worker

    For setup, select the following options:

    • For What would you like to start with?, choose Hello World example.
    • For Which template would you like to use?, choose Hello World Worker.
    • For Which language do you want to use?, choose JavaScript.
    • For Do you want to use git for version control?, choose Yes.
    • For Do you want to deploy your application?, choose No (we will be making some changes before deploying).

  2. Change to the project directory:

    Terminal window
    $ cd device-posture-worker

  3. Copy-paste the following code into src/index.js. Be sure to replace <your-team-name> with your Zero Trust team name.

    index.js
    import { parse } from "cookie";
    export default {
      async fetch(request, env, ctx) {
        // The name of the cookie
        const COOKIE_NAME = "CF_Authorization";
      const CF_GET_IDENTITY = "https://<your-team-name>.cloudflareaccess.com>/cdn-cgi/access/get-identity";
        const cookie = parse(request.headers.get("Cookie") || "");
        if (cookie[COOKIE_NAME] != null) {
        try {
        let id = await (await fetch(CF_GET_IDENTITY, request)).json()
        let diskEncryptionStatus = false;
        let firewallStatus = false;
    

        for (const checkId in id.devicePosture) {
          const check = id.devicePosture[checkId];
          if (check.type === "disk_encryption") {
            console.log(check.type)
            diskEncryptionStatus = check.success;
          }
          if (check.type === "firewall") {
            console.log(check.type)
            firewallStatus = check.success;
            break;
          }
        }
        //clone request (immutable otherwise) and insert posture values in new header set
        let newRequest = await new Request(request)
        newRequest.headers.set("Cf-Access-Firewall-Activated", firewallStatus)
        newRequest.headers.set("Cf-Access-Disk-Encrypted", firewallStatus)
    

        //sent modified request to origin
        return await fetch(newRequest)
    

        } catch (e) {
        console.log(e)
        return await fetch(request)
        }
        }
        return await fetch(request)
      },
    };

2. View the user’s identity

The script in index.js uses the get-identity endpoint to fetch a user’s complete identity from a Cloudflare Access authentication event. To view a list of available data fields, log in to your Access application and append /cdn-cgi/access/get-identity to the URL. For example, if www.example.com is behind Access, go to https://www.example.com/cdn-cgi/access/get-identity.

Below is an example of a user identity that includes the disk_encryption and firewall posture checks. The Worker inserts the posture check results into the request headers Cf-Access-Firewall-Activated and Cf-Access-Disk-Encrypted.

Example user identity
{
  "id": "P51Tuu01fWHMBjIBvrCK1lK-eUDWs2aQMv03WDqT5oY",
  "name": "John Doe",
  "email": "[email protected]",
  "amr": [
    "pwd"
  ],
  "oidc_fields": {
    "principalName": "XXXXXX_cloudflare.com#EXT#@XXXXXXcloudflare.onmicrosoft.com"
  },
  "groups": [
    {
      "id": "fdaedb59-e9be-4ab7-8001-3e069da54185",
      "name": "XXXXX"
    }
  ],
  "idp": {
    "id": "b9f4d68e-dac1-48b0-b728-ae05a5f0d4b2",
    "type": "azureAD"
  },
  "geo": {
    "country": "FR"
  },
  "user_uuid": "ce40d564-c72f-475f-a9b8-f395f19ad986",
  "account_id": "121287a0c6e6260ec930655e6b39a3a8",
  "iat": 1724056537,
  "devicePosture": {
    "f6f9391e-6776-4878-9c60-0cc807dc7dc8": {
      "id": "f6f9391e-6776-4878-9c60-0cc807dc7dc8",
      "schedule": "5m",
      "timestamp": "2024-08-19T08:31:59.274Z",
      "description": "",
      "type": "disk_encryption",
      "check": {
        "drives": {
          "C": {
            "encrypted": true
          }
        }
      },
      "success": false,
      "rule_name": "Disk Encryption - Windows",
      "input": {
        "requireAll": true,
        "checkDisks": []
    },
    "a0a8e83d-be75-4aa6-bfa0-5791da6e9186": {
      "id": "a0a8e83d-be75-4aa6-bfa0-5791da6e9186",
      "schedule": "5m",
      "timestamp": "2024-08-19T08:31:59.274Z",
      "description": "",
      "type": "firewall",
      "check": {
        "firewall": false
      },
      "success": false,
      "rule_name": "Local Firewall Check - Windows",
      "input": {
        "enabled": true
      }
    }
    ...
  }

3. Route the Worker to your application

In wrangler.toml, set up a route that maps the Worker to your Access application domain:

route = { pattern= "app.example.com/*", zone_name="example.com"}

4. Deploy the Worker

Terminal window
npx wrangler deploy

The Worker will now insert the Cf-Access-Firewall-Activated and Cf-Access-Disk-Encrypted headers into requests that pass your application’s Access policies.

Example request headers
{
  "headers": {
    "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7",
    "Accept-Encoding": "gzip",
    "Accept-Language": "en-US,en;q=0.9,fr-FR;q=0.8,fr;q=0.7,en-GB;q=0.6",
    "Cf-Access-Authenticated-User-Email": "[email protected]",
    "Cf-Access-Disk-Encrypted": "false",
    "Cf-Access-Firewall-Activated": "false",
    "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36"
  }
}

You can verify that these headers are received by the origin server.

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