stackpilot/backend/auth.py

"""JWT auth + user management."""
from __future__ import annotations

from datetime import datetime, timedelta, timezone
from typing import Optional

from fastapi import Depends, HTTPException, Request, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from passlib import exc
from passlib.context import CryptContext
from sqlmodel import Session, select

from config import settings
from database import get_session
from models.user import User
from services import api_token_service

pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login", auto_error=False)


# --- password helpers ---


def hash_password(password: str) -> str:
    return pwd_context.hash(password)


def verify_password(plain: str, hashed: str) -> bool:
    """Does this password match the stored hash?

    A hash passlib cannot parse means "no", not an exception. Accounts that
    sign in through the identity provider deliberately store an unusable
    marker instead of a hash (see services/oidc_service.py), and a password
    attempt against one of those has to be a clean rejection rather than a 500
    — which is also what any other corrupt row deserves.
    """
    try:
        return pwd_context.verify(plain, hashed)
    except (ValueError, TypeError, exc.PasslibSecurityError, exc.UnknownHashError):
        return False


# --- token helpers ---


def token_version_of(user: User) -> int:
    """A user's current token version, tolerating a NULL from an older schema."""
    return int(user.token_version or 1)


def _create_token(user: User, token_type: str, expires: timedelta) -> str:
    now = datetime.now(timezone.utc)
    payload = {
        "sub": user.username,
        "role": user.role,
        "type": token_type,
        # Minted-at authority version. Checked on every request, so bumping it
        # revokes every token this user already holds.
        "ver": token_version_of(user),
        "iat": now,
        "exp": now + expires,
    }
    return jwt.encode(payload, settings.SECRET_KEY, algorithm=settings.ALGORITHM)


def create_access_token(user: User) -> str:
    return _create_token(
        user, "access", timedelta(minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES)
    )


def create_refresh_token(user: User) -> str:
    return _create_token(
        user, "refresh", timedelta(days=settings.REFRESH_TOKEN_EXPIRE_DAYS)
    )


def bump_token_version(user: User) -> None:
    """Invalidate every token this user currently holds.

    Called whenever their authority changes — password, role, active flag — so
    a compromised account is actually cut off instead of staying usable until
    the tokens expire on their own. The caller commits.
    """
    user.token_version = token_version_of(user) + 1


def decode_token(token: str, expected_type: str = "access") -> dict:
    try:
        payload = jwt.decode(
            token, settings.SECRET_KEY, algorithms=[settings.ALGORITHM]
        )
    except JWTError as exc:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid token",
        ) from exc
    if payload.get("type") != expected_type:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Wrong token type",
        )
    return payload


# --- user lookups ---


def resolve_token_user(session: Session, payload: dict) -> Optional[User]:
    """The live user a token payload refers to, or None if it is no longer valid.

    Deliberately re-reads the database rather than trusting the token's claims:
    the role in a token is a snapshot from when it was minted, and an account
    can be disabled or have its password reset at any point afterwards.
    """
    user = get_user(session, payload.get("sub", ""))
    if not user or not user.is_active:
        return None
    if int(payload.get("ver", 0)) != token_version_of(user):
        return None
    return user


def get_user(session: Session, username: str) -> Optional[User]:
    return session.exec(select(User).where(User.username == username)).first()


def authenticate(session: Session, username: str, password: str) -> Optional[User]:
    user = get_user(session, username)
    if not user or not user.is_active:
        return None
    if not verify_password(password, user.hashed_password):
        return None
    return user


def users_exist(session: Session) -> bool:
    return session.exec(select(User)).first() is not None


# --- FastAPI dependencies ---


def get_current_user(
    request: Request,
    token: Optional[str] = Depends(oauth2_scheme),
    session: Session = Depends(get_session),
) -> User:
    if not token:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Not authenticated",
            headers={"WWW-Authenticate": "Bearer"},
        )
    # An API token is not a JWT and must not be fed to the decoder — it is
    # recognised by its prefix and looked up instead.
    if api_token_service.looks_like_token(token):
        resolved = api_token_service.resolve(session, token)
        if not resolved:
            raise HTTPException(
                status_code=status.HTTP_401_UNAUTHORIZED,
                detail="This API token is not valid (unknown, expired or revoked)",
            )
        row, user = resolved
        api_token_service.touch(session, row)
        # Stashed rather than folded into the User: mutating the role on a
        # session-attached row would be written back to the database the next
        # time anything commits that user.
        request.state.api_token = row
        return user

    request.state.api_token = None
    payload = decode_token(token, "access")
    user = resolve_token_user(session, payload)
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Session is no longer valid — sign in again",
        )
    return user


def current_api_token(request: Request):
    """The API token this request was authenticated with, if any."""
    return getattr(request.state, "api_token", None)


def require_admin_role(user: User) -> User:
    """Role check split out so the WebSocket routes can reuse it."""
    if user.role != "admin":
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Admin privileges required",
        )
    return user


def require_admin(
    request: Request, user: User = Depends(get_current_user)
) -> User:
    require_admin_role(user)
    row = current_api_token(request)
    if row and api_token_service.effective_role(row, user) != "admin":
        # The owner is an admin but this token was issued read-only, which is
        # the whole point of handing one to a monitoring script.
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="This API token is read-only",
        )
    return user


def require_session(
    request: Request, user: User = Depends(get_current_user)
) -> User:
    """An interactive session, not an API token.

    Guards the routes that mint or revoke credentials — API tokens and user
    accounts. A leaked CI token should be able to do the job it was issued for,
    not quietly grant itself permanent access that outlives its own revocation.
    """
    if current_api_token(request) is not None:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="This action requires a signed-in session, not an API token",
        )
    return user


def require_admin_session(
    request: Request, user: User = Depends(require_admin)
) -> User:
    return require_session(request, user)