FastAPI Session-Based Authentication

Architecture Overview

Auth Flow: Client → HTTPBearer → AuthService.check_session() → User
OAuth Flow: Google → /oauth/google/callback → AuthService.oauth_login() → Session → Redirect
Layers: Repository (data) → Service (logic) → Router (endpoints) → Dependencies (guards)

User Model

# app/user/models.py
import uuid
from argon2 import PasswordHasher
from argon2.exceptions import VerifyMismatchError
from sqlalchemy import String
from sqlalchemy.orm import Mapped, mapped_column