Per Diem Calculator

A comprehensive web application for calculating and tracking travel expenses with automatic per diem rate lookup using the GSA API.

Features

🔐 Secure Authentication

• Single sign-on with environment-based credentials
• Session management to protect API key from rate limiting
• Secure cookie handling with HTTPS in production

💰 Per Diem Integration

• Automatic lookup of GSA per diem rates by city and date
• Support for both lodging and meals & incidentals
• Real-time rate calculation based on expense type
• Uses official GSA API with environment-secured API key

📊 Expense Management

• Add expenses one by one (similar to Excel entry)
• Categorize as Lodging or Food expenses
• Automatic per diem calculation for each expense
• Track receipt amounts vs. per diem allowances

📋 Data Organization

• Clean, organized table display
• Separate sections for Lodging and Food expenses
• Running totals and grand total calculation
• Export to CSV functionality

🌟 Modern Interface

• Responsive design that works on all devices
• Beautiful gradient styling
• Real-time summary cards showing totals
• Intuitive form-based data entry

Usage

1. Login: Use the credentials to log in securely. Ensure you have the correct environment variables set up for authentication.

2. Add Expenses:

   • Select expense type (Lodging or Food)
   • Enter date, establishment name, and receipt amount
   • Enter city and state (2-letter code)
   • Click "Get Per Diem Rate" to automatically fetch the GSA rate
   • Add optional notes
   • Click "Add Expense" to save

3. View & Manage:

   • All expenses are displayed in an organized table
   • Summary cards show running totals
   • Delete individual expenses as needed
   • Export all data to CSV format

4. Export Data: Click "Export to CSV" to download your expense report

API Integration

This application uses the official GSA Per Diem API:

• Base URL: https://api.gsa.gov/travel/perdiem/v2
• API Key: Securely stored server-side
• Rate Limiting: Protected by authentication system

Technical Details

• Backend: Node.js with Express.js
• Frontend: Vanilla JavaScript with modern ES6+ features
• Storage: Local browser storage for data persistence
• Authentication: Express sessions
• Node Version: 22+ (AWS compatible)

Security

• API key is stored server-side only
• Session-based authentication
• Protected routes require login
• No sensitive data exposed to client

Deployment Steps

1. Create App Runner Service:

   • Go to AWS App Runner console
   • Create new service
   • Choose "Source code repository"

2. Configure Build:

   • Runtime: Node.js 22
   • Build command: npm ci --only=production
   • Start command: node server.js
   • Port: 3002

3. Set Environment Variables:

   • In App Runner service configuration
   • Add all required environment variables
   • CRITICAL: Never commit .env file to source control

4. Configure Security:

   • HTTPS automatically enabled
   • Secure session cookies in production
   • Environment-based credential management

Security Features

• ✅ Environment variables for all secrets
• ✅ HTTPS enforced in production
• ✅ Secure session cookies with proper SameSite settings
• ✅ No hardcoded credentials in source code
• ✅ Input validation and sanitization

Notes

• Data persists in browser local storage
• Application requires internet connection for GSA API calls
• Designed for single-user use with environment-configured credentials
• Production-ready with AWS App Runner deployment support