Add auth layer with Google/GitHub OAuth and Stripe subscription payments

[Copilot]

Adds authentication via OAuth providers and Stripe integration for monthly subscription payments to access premium content.

Authentication (NextAuth.js)

• Google and GitHub OAuth providers
• JWT session strategy with subscription status tracking
• Custom sign-in page with provider buttons
• Header component with auth status, avatar, and premium badge

Stripe Payments

• Monthly subscription checkout ($9.99/month)
• Webhook handler for subscription lifecycle events (checkout.session.completed, customer.subscription.updated/deleted, invoice.payment_failed)
• Customer portal for subscription management
• Test card numbers displayed on subscription page for development

Configuration

• .env.example template with all required variables
• Updated SETUP.md with OAuth and Stripe setup instructions
• next.config.ts updated to support API routes (static export disables auth/payments)

# Required environment variables
NEXTAUTH_SECRET=...
GOOGLE_CLIENT_ID=... / GITHUB_ID=...
STRIPE_SECRET_KEY=...
STRIPE_MONTHLY_PRICE_ID=...

Note: Subscription data uses in-memory storage for demo purposes. Replace with database for production.

GitHub Pages Deployment

Created a custom build script (scripts/build-github-pages.sh) that enables GitHub Pages deployment with static export:

• Temporarily excludes API routes during static export build (incompatible with static sites)
• Sets DEPLOY_ENV=github-pages environment variable to enable static export mode
• Restores API routes after build completes
• GitHub Actions workflow configured to use this script for automated deployments

This allows the site to be deployed to GitHub Pages (without auth/payment features) while maintaining full functionality when deployed to platforms supporting Next.js API routes (Vercel, Netlify, etc.).

Screenshots

Sign In	Subscription	Test Cards

[!WARNING]

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create auth layer + connect to Stripe for payments</issue_title>
<issue_description>- Login with Google or GitHub

• Connection to Stripe to collect payment (monthly subscription to access reponses to questions)
• Make Stripe integration testable with a fake card number in test mode somehow</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create auth layer + connect to Stripe for payments #10

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[mbianchidev]

@copilot ensure that Actions deploys with the environment set as github-pages

[Copilot]

@copilot ensure that Actions deploys with the environment set as github-pages

Updated in commit 4625f1a. Created a build script that sets DEPLOY_ENV=github-pages and temporarily excludes API routes during static export build. The workflow now uses scripts/build-github-pages.sh which enables static export mode while preserving auth/payment functionality for non-static deployments.