Add GitHub App setup guide and webhook integration with ping/pong test command

[Copilot]

Provides comprehensive GitHub App setup documentation and implements a webhook endpoint with JWT authentication to enable bot interactions with repositories.

Documentation

GITHUB_APP_SETUP.md - Complete setup guide covering:

• GitHub App creation and configuration
• Private key generation and security
• Webhook URL setup with ngrok for local testing
• Permission scoping (Issues, PRs, Contents)
• Environment variable configuration
• Troubleshooting common issues

Implementation

Webhook Endpoint (/aibot/webhook/)

• HMAC-SHA256 signature verification for security
• Event routing: ping, issue_comment, pull_request
• CSRF-exempt with signature-based auth

GitHub App Authentication (aibot/github_utils.py)

• JWT token generation using RSA private key
• Installation access token management
• API client for creating comments
• Specific error messages for auth failures (401), missing installations (404), permission issues (403)

Ping/Pong Command

• Responds to /ping in issue comments with "🏓 Pong! The GitHub App is working correctly."
• Validates webhook flow end-to-end

Configuration

Environment variables required:

GITHUB_APP_ID=123456
GITHUB_APP_PRIVATE_KEY_PATH=/path/to/private-key.pem
GITHUB_WEBHOOK_SECRET=your-webhook-secret
GITHUB_APP_INSTALLATION_ID=7891011

Added *.pem to .gitignore to prevent private key leaks.

Testing

Example webhook payload handling:

# POST /aibot/webhook/
# Headers: X-GitHub-Event: issue_comment, X-Hub-Signature-256: sha256=...
{
  "action": "created",
  "comment": {"body": "/ping"},
  "issue": {"number": 123},
  "repository": {"name": "repo", "owner": {"login": "owner"}}
}
# Response: Creates comment "🏓 Pong! The GitHub App is working correctly."

6 unit tests covering signature validation, event routing, command processing, and error handling.

Original prompt

create instructions on how to setup a github app and link it to this repo add a ping / pong command that tests that everything is working

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