The tutorial provides a comprehensive guide on securing a GenAI image generation service using Node.js, Express, and PropelAuth, which facilitates API key validation and user management. It details setting up a system for users to sign up for a free 7-day trial, upgrade to a paid plan, and generate images with validated API keys, with trial expiration dates checked before processing requests. The guide outlines creating an Express API with endpoints to simulate Stripe payment processing and image creation, utilizing PropelAuth’s API Key Authentication and custom user properties to manage user plans. The tutorial also explains setting up a Stripe webhook to update user plans based on subscription events and implementing an image creation endpoint to validate API keys and user eligibility based on their plan or trial status. Additionally, it highlights the use of environment files for secure API key management and concludes with bonus insights on tracking API key signups through PropelAuth's user audit logs, offering a practical approach to implementing a secure and efficient user authentication and management system for API services.