Project-SDE-WP-Suite/server/auth.py

"""Authentication for the Work Package Suite.

A self-contained username/password login. Passwords are stored only as bcrypt
hashes; a successful login issues a signed JWT that rides in an HttpOnly cookie
(`wp_session`). Because the token is signed and self-validating, there is no
server-side session store — every request is checked by verifying the cookie's
signature and expiry (see `auth_gate` and `get_current_user`).

Security model:
  • The real boundary is `auth_gate` (middleware in app.py): every /api/ data
    route is refused with 401 unless a valid session cookie is present.
  • The cookie is HttpOnly (JS can't read it → XSS can't steal the session),
    SameSite=Lax (blunts CSRF), and Secure whenever the request arrives over
    HTTPS (detected via X-Forwarded-Proto behind NGINX).
  • The signing secret comes from AUTH_SECRET_KEY. In production this MUST be
    set; if it is missing we fall back to a random per-process key (which logs a
    warning and invalidates every session on restart) so dev still works.

Roles: 'admin' (may manage users) and 'user'.
"""
import os
import secrets
import logging
from datetime import datetime, timedelta, timezone
from typing import Optional

import bcrypt
import jwt
from fastapi import Depends, HTTPException, Request, Response, status
from sqlalchemy import select, func
from sqlalchemy.orm import Session

from .db import get_db
from . import models

log = logging.getLogger("wpsuite.auth")

COOKIE_NAME = "wp_session"
JWT_ALG = "HS256"
# How long a login lasts before the user must sign in again.
SESSION_HOURS = int(os.getenv("AUTH_SESSION_HOURS", "12"))

# Paths under /api that do NOT require a session (login itself, health, docs).
_EXEMPT_PREFIXES = ("/api/auth/",)
_EXEMPT_EXACT = {
    "/api/health",
    "/api/docs",
    "/api/openapi.json",
    "/api/docs/oauth2-redirect",
    "/api/redoc",
}


def _load_secret() -> str:
    s = os.getenv("AUTH_SECRET_KEY")
    if s:
        return s
    # No secret configured: generate an ephemeral one so the app still runs in
    # dev. Sessions won't survive a restart, and this is unsafe across multiple
    # workers — production must set AUTH_SECRET_KEY.
    log.warning(
        "AUTH_SECRET_KEY is not set — using a random ephemeral key. "
        "Logins will reset on restart and break across multiple workers. "
        "Set AUTH_SECRET_KEY in the environment for production."
    )
    return secrets.token_urlsafe(48)


SECRET_KEY = _load_secret()


# ── password hashing ──────────────────────────────────────────────────────────
def hash_password(plain: str) -> str:
    # bcrypt operates on at most 72 bytes; longer inputs are truncated by the
    # algorithm. Encode explicitly so non-ASCII passwords hash consistently.
    return bcrypt.hashpw(plain.encode("utf-8")[:72], bcrypt.gensalt()).decode("ascii")


def verify_password(plain: str, hashed: str) -> bool:
    if not hashed:
        return False
    try:
        return bcrypt.checkpw(plain.encode("utf-8")[:72], hashed.encode("ascii"))
    except (ValueError, TypeError):
        return False


# ── tokens ──────────────────────────────────────────────────────────────────
def create_token(user: "models.User") -> str:
    now = datetime.now(timezone.utc)
    payload = {
        "sub": user.id,
        "username": user.username,
        "role": user.role,
        "iat": now,
        "exp": now + timedelta(hours=SESSION_HOURS),
    }
    return jwt.encode(payload, SECRET_KEY, algorithm=JWT_ALG)


def decode_token(token: str) -> Optional[dict]:
    """Return the token claims if the signature and expiry are valid, else None."""
    try:
        return jwt.decode(token, SECRET_KEY, algorithms=[JWT_ALG])
    except jwt.PyJWTError:
        return None


# ── cookie helpers ────────────────────────────────────────────────────────────
def _is_https(request: Request) -> bool:
    # Behind NGINX, TLS is terminated at the proxy and forwarded as plain HTTP,
    # so trust X-Forwarded-Proto (set in nginx-wp-suite.conf) when present.
    xfp = request.headers.get("x-forwarded-proto", "")
    if xfp:
        return xfp.split(",")[0].strip().lower() == "https"
    return request.url.scheme == "https"


def set_session_cookie(response: Response, request: Request, token: str) -> None:
    response.set_cookie(
        key=COOKIE_NAME,
        value=token,
        max_age=SESSION_HOURS * 3600,
        httponly=True,
        secure=_is_https(request),
        samesite="lax",
        path="/",
    )


def clear_session_cookie(response: Response) -> None:
    response.delete_cookie(COOKIE_NAME, path="/")


# ── request gate (used as middleware in app.py) ─────────────────────────────────
def _needs_auth(path: str) -> bool:
    if not path.startswith("/api/"):
        return False  # static assets are served by NGINX, not this app
    if path in _EXEMPT_EXACT:
        return False
    return not any(path.startswith(p) for p in _EXEMPT_PREFIXES)


def is_request_authenticated(request: Request) -> Optional[dict]:
    """Validate the session cookie on a raw request. Returns claims or None.
    Used by the middleware gate, which has no dependency-injection context."""
    token = request.cookies.get(COOKIE_NAME)
    if not token:
        return None
    return decode_token(token)


# ── dependencies (used inside route handlers) ───────────────────────────────────
def get_current_user(request: Request, db: Session = Depends(get_db)) -> "models.User":
    """Resolve the logged-in user from the session cookie, or raise 401.

    Unlike the middleware gate (which only checks the token signature), this also
    confirms the account still exists and is active — so disabling a user takes
    effect on their next request."""
    claims = is_request_authenticated(request)
    if not claims:
        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Not authenticated")
    user = db.get(models.User, claims.get("sub"))
    if not user or not user.is_active:
        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Account is inactive")
    return user


def require_admin(user: "models.User" = Depends(get_current_user)) -> "models.User":
    if user.role != "admin":
        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Admin access required")
    return user


# ── account helpers (shared by routes and the CLI) ──────────────────────────────
def find_user(db: Session, username: str) -> Optional["models.User"]:
    """Look up by username, case-insensitively (also matches on email)."""
    uname = (username or "").strip().lower()
    if not uname:
        return None
    return db.scalars(
        select(models.User).where(
            (func.lower(models.User.username) == uname)
            | (func.lower(models.User.email) == uname)
        )
    ).first()