Auth Code Flow with PKCE: A Comprehensive Guide to API-Based Integration (Without Keycloak Redirect URL)

Implementation Overview

Before we dive into the step-by-step implementation guide, let’s take a high-level look at the process:

1. The client (your application) requests authorization from the resource owner (the user).
2. The resource owner grants consent, and the client receives an authorization code.
3. The client generates a code verifier and a code challenge.
4. The client sends the code challenge with the authorization request.
5. The authorization server responds with an authorization code.
6. The client uses the code verifier to validate the authorization code response.
7. The client exchanges the authorization code for an access token.
8. The client uses the access token to access the protected API resources.

Step-by-Step Implementation Guide

Now that we’ve covered the basics, let’s get started with the implementation:

Step 1: Client Registration

To begin, you’ll need to register your client (application) with the authorization server. You’ll receive a client ID and a client secret, which will be used to identify your client.

curl -X POST \
  https://authorization-server.com/register \
  -H 'Content-Type: application/json' \
  -d '{
        "client_name": "My Awesome App",
        "redirect_uri": "https://myapp.com/callback"
      }'

Step 2: Authorization Request

Next, the client (your application) requests authorization from the resource owner (the user). You’ll need to include the client ID, response type (code), and redirect URI.

https://authorization-server.com/auth?
  client_id=YOUR_CLIENT_ID&
  response_type=code&
  redirect_uri=https://myapp.com/callback&
  scope=openid%20profile%20email&
  state=YOUR_STATE_VALUE

Step 3: Generate Code Verifier and Code Challenge

After the user grants consent, the client generates a code verifier and a code challenge. The code verifier is a high-entropy string, and the code challenge is a base64url-encoded hash of the code verifier.

// Generate code verifier
const codeVerifier = generateRandomString(43);

// Generate code challenge
const codeChallenge = base64url.encode(hash(codeVerifier));

Step 4: Authorization Code Request

The client sends the code challenge with the authorization request. The authorization server will respond with an authorization code.

curl -X POST \
  https://authorization-server.com/token \
  -H 'Content-Type: application/x-www-form-urlencoded' \
  -d 'grant_type=authorization_code&
       code_challenge_method=S256&
       code_challenge=YOUR_CODE_CHALLENGE&
       redirect_uri=https://myapp.com/callback&
       client_id=YOUR_CLIENT_ID
      '

Step 5: Validate Authorization Code Response

The client uses the code verifier to validate the authorization code response. If the response is valid, the client can exchange the authorization code for an access token.

// Validate authorization code response
if (hash(authorizationCode) === codeVerifier) {
  // Exchange authorization code for access token
  curl -X POST \
    https://authorization-server.com/token \
    -H 'Content-Type: application/x-www-form-urlencoded' \
    -d 'grant_type=authorization_code&
         code=YOUR_AUTHORIZATION_CODE&
         redirect_uri=https://myapp.com/callback&
         client_id=YOUR_CLIENT_ID&
         client_secret=YOUR_CLIENT_SECRET
        '
}

Step 6: Access Protected API Resources

Finally, the client uses the access token to access the protected API resources.

curl -X GET \
  https://api.example.com/data \
  -H 'Authorization: Bearer YOUR_ACCESS_TOKEN'

Conclusion

Implementing Auth Code Flow with PKCE for API-based integration without a Keycloak redirect URL may seem daunting at first, but by following this step-by-step guide, you should be able to integrate this secure authorization flow into your application.

Remember to keep your client secret secure, and always validate the authorization code response to ensure the integrity of your application.

Frequently Asked Questions

Still have questions? Here are some common FAQs:

By now, you should have a solid understanding of Auth Code Flow with PKCE and how to implement it for API-based integration without a Keycloak redirect URL. Happy coding!

Frequently Asked Questions

Get answers to your burning questions about Auth Code flow with PKCE with API-based integration (without Keycloak redirect URL).