Welcome, Candidate!

This project is a take-home exercise to help us understand your engineering skills, particularly in the context of payment systems.

The Scenario

You are an engineer at "Mystic Wares," an e-commerce company selling high-end (and slightly magical) sunglasses and headphones. Our current checkout process is a placeholder. Your task is to build a real payment integration using the Adyen payments platform.

Core Task (2-3 hours)

Your primary goal is to implement a complete payment flow for a credit card payment. The existing Java/Spring Boot application provides a basic structure, but the core payment logic is missing.

You will need to:

1. Implement the Checkout Flow:
   • Fetch available payment methods from Adyen.
   • Initiate a payment request when the user clicks "Pay".
   • Handle the 3D Secure 2 authentication challenge.
   • Process the final payment result and redirect the user to a success or failure page.
2. Handle Payment Updates:
   • Implement a webhook endpoint to receive asynchronous payment updates from Adyen.
   • Ensure the webhook is secure by validating the HMAC signature.

The application should be fully functional for a test credit card payment upon completion.

Bonus Tasks (Optional, 1-2 hours)

If you have extra time and want to showcase more of your skills, please choose one or two of the following:

• Add a New Payment Method: Implement iDeal or Klarna, which are popular in our target market (the Netherlands). This will require handling different payment flows.
• Implement Recurring Payments (Tokenization): Our marketing team wants to launch a "Sunglass of the Month" club. Implement the logic to securely store a customer's card details (tokenization) and make a subsequent payment using the stored token.
• Implement Pre-authorisation: For high-value orders, we want to pre-authorise a card, and then "capture" the final amount later when the order ships. Implement the pre-authorisation and capture flow.
• Testing: The project is missing complete tests. Add unit or integration tests to validate the payment logic you've built.
• Code Critique & Suggestions: What would you improve in this codebase if you had more time? Add your thoughts in a SUGGESTIONS.md file. We're interested in your thoughts on architecture, security, and overall code quality.

Getting Started

1. The backend is a Java Spring Boot application. You can run it with ./gradlew bootRun.
2. You will need an Adyen test account to get API credentials. You can sign up here: Adyen Signup.
3. Configure your credentials in src/main/resources/application.properties.

What We're Looking For

• Architecture and API Design: Is the solution well-structured? Are the API endpoints clear and logical?
• Correctness: Does the payment flow work as expected?
• Code Quality: Is the code clean, maintainable, and easy to understand?
• Security: Have you considered security best practices, such as HMAC validation and handling credentials?
• Problem Solving: How did you approach the open-ended tasks?

Please submit your solution by providing a link to a private Git repository showing your commit history. Good luck!