Standard OAuth Agent

Overview

The role of the OAuth Agent in the below diagram is to handle the OpenID Connect flow for Single Page Applications (SPA). This includes issuing of secure cookies for the browser and managing follow-on operations for token refresh, retrieving user info and signing out:

This implementation is coded in Node.js and implements the Authorization Code Flow with PKCE using a client secret. The result is that only the strongest HTTP Only, SameSite=strict cookies are used in the browser, while JWT access tokens are used in a standard way by APIs.

OAuth Agent Operations

The following operations represent the OAuth Agent's API interface, and all of these are designed to serve SPAs via Ajax requests from the browser. This enables the SPA to fully control behavior such as when redirects occur:

An OAuth Agent is a tricky API to develop, since its main focus is on browser and OAuth infrastructure:

Get the Code

First get the code, which is a standard Node.js API that uses the Express HTTP server, and the repository contains both code and test resources:

The OAuth logic for the OAuth Agent can be studied and adapted if needed. The controller source files provide an outline of processing, including cookie issuing. To understand the main interaction with the Authorization Server, see the authorizeUrl and getToken modules within the lib folder.

Configure Development URLs

When running on a development computer, the OAuth Agent is configured to use the following base URLs. The default setup uses plain HTTP URLs in order to simplify infrastructure on a development computer, though of course the OAuth Agent should be updated to use SSL for deployed environments:

For URLs to work you will need to add the following entries to the local computer's hosts file:

127.0.0.1  api.example.local login.example.local
:1 localhost

Run the OAuth Agent

This is done in the standard Node.js manner, after which the API's HTTP endpoints are available for a client to call:

npm install
npm start

You can then simulate a request from the SPA via the following test command, to ensure that connectivity is working:

curl -X POST http://api.example.local:8080/oauth-agent/login/start \
-H "origin: http://www.example.local" | jq

Run Integration Tests

When working on the OAuth Agent as an API it is useful to initially avoid a browser and use a test driven approach. Integration tests use Wiremock to mock the endpoints of the Curity Identity Server. First ensure that a Java runtime is installed, then run this command:

npm run wiremock

Integration tests are then run with the standard npm test command and result in the following output:

Run End-to-End Tests

In order to run tests that use an instance of the Curity Identity Server, first ensure that the following components are installed:

• Node.js
• Docker Desktop
• jq

You will also need a license file for the Curity Identity Server. If you do not have one you can get a free community license from the Curity Developer Portal by signing in with your GitHub account. Copy the license file into the test/idsvr folder and run the following commands, to spin up a Docker based instance:

cd test/idsvr
./deploy.sh

You can then log in to the Admin UI with credentials admin / Password1 to view client configuration details. OAuth requests on behalf of the SPA are initiated from the OAuth Agent, which uses a client secret when it calls the Authorization Server:

Then run the following script based client, which sends the same HTTP requests as an SPA, but avoids the need to continually switch to a browser and extract values such as authorization codes. This scripted client uses the popular curl and jq tools:

cd test
./test-oauth-agent.sh

The script runs a complete SPA workflow, using a preconfigured user account shipped with the Docker deployment. This begins with a login, then continues with refresh, user info and claims requests, finishing with a logout. This fast feedback will enable any coding bugs in your own OAuth Agent to be quickly found and ironed out:

OpenID Connect Messages

The OAuth Agent returns front channel request URLs to the SPA, which then updates the browser location to this URL, to begin the user authentication process. At this point, the OAuth Agent has also written a temporary secure cookie containing state and code_verifier values.

GET http://login.example.local:8443/oauth/v2/oauth-authorize
    ?client_id=spa-client
    &redirect_uri=http%3A%2F%2Fwww.example.com%2F
    &response_type=code
    &code_challenge=l9QIPE4TFgW2y7STZDSWQ4Y4CQpO8W6VtELopzYHdNg
    &code_challenge_method=S256
    &state=NlAoISfdL1DxPdNGFBljlVuB1GDjgGARmqDcxtHhV8iKNYu6ECS2KOavDHpI3eLN
    &scope=openid%20profile

When authentication completes, the SPA sends the OAuth Agent the response URL containing the authorization code. The OAuth Agent then validates the response using the temporary cookie, then sends a back channel request to the Authorization Server, along with a client secret:

POST http://login.example.local:8443/oauth/v2/oauth-token

grant_type=authorization_code&
client_id=spa-client&
client_secret=Password1&
redirect_uri=http://www.example.com/&
code=YFFX2HmFNnrMS8alWIZH83oim9ZHgwRh&
code_verifier=ItJtBXUGtHs-3FpUHB8qW9uJ00XcwTfeiZdLGquawMg

Tokens returned in the response are then stored in HTTP Only encrypted secure cookies that are returned to the browser but not accessible from Javascript code. AES256 symmetric encryption is used to encrypt the cookies, with a key only known to the OAuth Agent.

Browser Integration

Once the OAuth Agent is working as expected and any code changes have been completed, you can deploy it and test with real SPAs running in the browser. This is simply a case of pointing the SPA to the base URL of the OAuth Agent in the deployed environment:

{
    "businessApiBaseUrl": "https://api.example.com/api",
    "oauth": {
        "oauthAgentBaseUrl": "https://api.example.com/oauth-agent"
    }
}

Conclusion

An OAuth Agent is a tricky component to develop, so Curity have provided a reference implementation that can be simply plugged in. If required companies can adapt Curity's implementation for their own purposes, by following the API development steps in this tutorial.