Multi-Backend User Authentication & Banking System

This project provides multiple backend implementations (Flask, FastAPI, Java Spring Boot, NestJS, and Go) of a user authentication system with banking functionality, all compatible with a single GUI client.

Project Structure

flask-fastapi-user-auth/
├── fastapi_server/
│   └── server.py          # FastAPI server with full banking functionality
├── flask_server/
│   └── server.py          # Flask server with basic authentication
├── java_server/           # Java Spring Boot server with full banking functionality
│   ├── src/main/java/com/example/banking/
│   │   ├── controller/    # REST controllers
│   │   ├── service/       # Business logic services
│   │   ├── model/         # Data models
│   │   └── config/        # Security and JWT configuration
│   ├── pom.xml           # Maven dependencies
│   └── users.json        # User data storage
├── nestjs_server/         # NestJS TypeScript server with full banking functionality
│   ├── src/
│   │   ├── auth/         # Authentication module
│   │   ├── account/      # Account management module
│   │   └── main.ts       # Application entry point
│   ├── package.json      # Node.js dependencies
│   └── users.json        # User data storage
├── go_server/            # Go server with full banking functionality
│   ├── main.go          # Main application file
│   ├── go.mod           # Go module dependencies
│   └── users.json        # User data storage
├── client.py             # Universal GUI client for all backends
├── requirements.txt      # Python dependencies
└── readme.md            # This file

Features

Authentication

• User registration and login
• JWT token-based authentication
• Password hashing with bcrypt

Banking Operations (All Backends)

• Create Account: Create a new bank account with initial balance
• Deposit: Add money to your account
• Withdraw: Remove money from your account (with balance validation)
• Transfer: Send money to another account
• Close Account: Close your account (requires zero balance)
• Account Info: View account details and balance

Security Features

• Unique account numbers (10-digit UUID-based)
• Balance validation for withdrawals and transfers
• Account ownership verification
• Token expiration handling

Installation

Python Backends (Flask & FastAPI)

1. Install Python dependencies:

pip install -r requirements.txt

Java Spring Boot Backend

1. Install Java 17 or higher
2. Install Maven 3.6 or higher
3. Navigate to the Java server directory:

cd java_server
mvn clean install

NestJS Backend

1. Install Node.js 18 or higher
2. Navigate to the NestJS server directory:

cd nestjs_server
npm install

Go Backend

1. Install Go 1.19 or higher
2. Navigate to the Go server directory:

cd go_server
go mod tidy

Running the Application

FastAPI Server (Python - Recommended)

cd fastapi_server
python server.py

Server runs on: http://127.0.0.1:5000

Java Spring Boot Server (Java - Full Featured)

cd java_server
mvn spring-boot:run

Server runs on: http://127.0.0.1:5000

NestJS Server (TypeScript - Full Featured)

cd nestjs_server
npm run start:dev

Server runs on: http://127.0.0.1:5000

Go Server (Go - Full Featured)

cd go_server
go run main.go

Server runs on: http://127.0.0.1:5000

Flask Server (Python - Full Featured)

cd flask_server
python server.py

Server runs on: http://127.0.0.1:5000 (default Flask port)

Universal Client Application

python client.py

Note: The client automatically detects and works with any of the five backend servers.

API Endpoints

Authentication Endpoints

• POST /register - Register a new user
• POST /login - Login and get JWT token
• GET /protected - Access protected resource

Banking Endpoints (All Backends)

• POST /accounts/create - Create a new account
• GET /accounts/my-account - Get account information
• POST /accounts/deposit - Deposit money
• POST /accounts/withdraw - Withdraw money
• POST /accounts/transfer - Transfer money to another account
• POST /accounts/close - Close account

Client Features

The GUI client provides:

• User registration and login
• Account creation with initial balance
• Deposit and withdrawal operations
• Money transfers between accounts
• Account closure
• Real-time balance updates
• Error handling and validation

Data Storage

Python Backends (Flask & FastAPI)

• User data: users.json
• Account data: accounts.json

Java Spring Boot Backend

• User data: users.json (BCrypt hashed passwords)
• Account data: accounts.json

Go Backend

• User data: users.json (BCrypt hashed passwords)
• Account data: accounts.json

All data files are created automatically when the servers start.

Usage Example

1. Start any backend server (FastAPI, Java Spring Boot, NestJS, Go, or Flask)
2. Run the client application
3. Register a new user or login
4. Create an account with initial balance (All backends support this)
5. Perform banking operations (deposit, withdraw, transfer)
6. View account information and balance

Backend Comparison

Feature	Flask	FastAPI	Java Spring Boot	NestJS	Go
Authentication	✅	✅	✅	✅	✅
Banking Operations	✅	✅	✅	✅	✅
JWT Tokens	✅	✅	✅	✅	✅
Password Hashing	✅	✅	✅ (BCrypt)	✅ (BCrypt)	✅ (BCrypt)
Data Storage	JSON	JSON	JSON	JSON	JSON
Performance	Good	Excellent	Excellent	Excellent	Excellent
Type Safety	✅	✅	✅	✅	✅
Language	Python	Python	Java	TypeScript	Go

Notes

• Each user can have only one active account
• Account numbers are unique 10-digit identifiers
• Transfers require valid recipient account numbers
• Accounts must have zero balance to be closed
• JWT tokens expire after 1 hour
• The client automatically adapts to different backend response formats
• Java Spring Boot and NestJS use BCrypt for enhanced password security
• Choose your preferred technology stack: Python (Flask/FastAPI), Java (Spring Boot), TypeScript (NestJS), or Go