blog.pyaqa.ru/app/presentation/web/auth.py

"""Web authentication routes for blog application.

This module provides OAuth2/OIDC authentication flow with Keycloak
for the web UI. Uses HTTP-only cookies for token storage.
"""

from typing import Any

import httpx
from fastapi import APIRouter, HTTPException, Request, Response
from fastapi.responses import RedirectResponse

from app.infrastructure.config.settings import settings

router = APIRouter(prefix="/auth", tags=["auth"])


def get_keycloak_login_url(redirect_uri: str) -> str:
    """Build Keycloak authorization URL.

    Args:
        redirect_uri: Callback URL after Keycloak authentication.

    Returns:
        Full Keycloak authorization endpoint URL.
    """
    base_url = f"{settings.kc.server_url}/realms/{settings.kc.realm}"
    return (
        f"{base_url}/protocol/openid-connect/auth"
        f"?client_id={settings.kc.client_id}"
        f"&response_type=code"
        f"&redirect_uri={redirect_uri}"
        f"&scope=openid"
    )


def get_keycloak_logout_url(redirect_uri: str) -> str:
    """Build Keycloak logout URL.

    Args:
        redirect_uri: URL to redirect after logout.

    Returns:
        Full Keycloak logout endpoint URL.
    """
    base_url = f"{settings.kc.server_url}/realms/{settings.kc.realm}"
    return (
        f"{base_url}/protocol/openid-connect/logout"
        f"?client_id={settings.kc.client_id}"
        f"&post_logout_redirect_uri={redirect_uri}"
    )


async def exchange_code_for_token(code: str, redirect_uri: str) -> dict[str, Any]:
    """Exchange authorization code for access token.

    Args:
        code: Authorization code from Keycloak.
        redirect_uri: Callback URL used during login.

    Returns:
        Token response containing access_token, refresh_token, etc.

    Raises:
        HTTPException: If token exchange fails.
    """
    token_url = f"{settings.kc.server_url}/realms/{settings.kc.realm}/protocol/openid-connect/token"

    data = {
        "grant_type": "authorization_code",
        "code": code,
        "client_id": settings.kc.client_id,
        "client_secret": settings.kc.client_secret,
        "redirect_uri": redirect_uri,
    }

    async with httpx.AsyncClient() as client:
        response = await client.post(token_url, data=data)

    if response.status_code != 200:
        raise HTTPException(status_code=400, detail="Failed to exchange code for token")

    result: dict[str, Any] = response.json()
    return result


@router.get("/login")
async def login(request: Request) -> RedirectResponse:
    """Redirect to Keycloak login page.

    Args:
        request: HTTP request object.

    Returns:
        RedirectResponse to Keycloak authorization endpoint.
    """
    callback_url = str(request.base_url).rstrip("/") + "/auth/callback"
    login_url = get_keycloak_login_url(callback_url)
    return RedirectResponse(url=login_url)


@router.get("/callback")
async def callback(request: Request, code: str | None = None) -> Response:
    """Handle OAuth callback from Keycloak.

    Exchanges authorization code for tokens and sets HTTP-only cookie.

    Args:
        request: HTTP request object.
        code: Authorization code from Keycloak.

    Returns:
        RedirectResponse to home page with token cookie set.

    Raises:
        HTTPException: If code is missing or token exchange fails.
    """
    if not code:
        raise HTTPException(status_code=400, detail="Authorization code not provided")

    callback_url = str(request.base_url).rstrip("/") + "/auth/callback"
    token_data = await exchange_code_for_token(code, callback_url)
    access_token = token_data.get("access_token")

    if not access_token:
        raise HTTPException(status_code=400, detail="No access token received")

    response = RedirectResponse(url="/web/", status_code=302)
    response.set_cookie(
        key="access_token",
        value=access_token,
        httponly=True,
        secure=not settings.is_dev,  # Secure in production
        samesite="lax",
        max_age=token_data.get("expires_in", 3600),
    )

    return response


@router.get("/logout")
async def logout(request: Request) -> Response:
    """Logout user and clear token cookie.

    Args:
        request: HTTP request object.

    Returns:
        RedirectResponse to Keycloak logout with cookie cleared.
    """
    home_url = str(request.base_url).rstrip("/") + "/web/"
    logout_url = get_keycloak_logout_url(home_url)

    response = RedirectResponse(url=logout_url)
    response.delete_cookie(key="access_token")

    return response