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```python
# AI Dev Tool: FastAPI Pydantic v2 Micro-SaaS Boilerplate
# Description: A production-ready boilerplate for building micro-SaaS applications using FastAPI and Pydantic v2
# Author: Elite Software Architect

from fastapi import FastAPI, Depends, HTTPException
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from pydantic import BaseModel, Field
from typing import Optional
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, Session

# Database Configuration
SQLALCHEMY_DATABASE_URL = "sqlite:///example.db"

# Create a database engine
engine = create_engine(SQLALCHEMY_DATABASE_URL)

# Create a configured "Session" class
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

# Create a base class for declarative class definitions
Base = declarative_base()

# Define a Pydantic model for user authentication
class User(BaseModel):
    """User authentication model"""
    username: str = Field(..., example="john_doe")
    email: str = Field(..., example="john@example.com")
    full_name: str

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