Rename the import package app to fluksio

A wheel whose top-level module is `app` collides with anything else in a
user's venv, so the package that is about to be published takes the name
it is published under. Only the Python package moves; the repo, the
Docker WORKDIR and the compose project keep theirs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/fluksio/crud.py

@@ -0,0 +1,59 @@
+from typing import Any
+
+from sqlmodel import Session, select
+
+from fluksio.core.security import get_password_hash, verify_password
+from fluksio.models import User, UserCreate, UserUpdate
+
+
+def create_user(*, session: Session, user_create: UserCreate) -> User:
+    db_obj = User.model_validate(
+        user_create, update={"hashed_password": get_password_hash(user_create.password)}
+    )
+    session.add(db_obj)
+    session.commit()
+    session.refresh(db_obj)
+    return db_obj
+
+
+def update_user(*, session: Session, db_user: User, user_in: UserUpdate) -> Any:
+    user_data = user_in.model_dump(exclude_unset=True)
+    extra_data = {}
+    if "password" in user_data:
+        password = user_data["password"]
+        hashed_password = get_password_hash(password)
+        extra_data["hashed_password"] = hashed_password
+    db_user.sqlmodel_update(user_data, update=extra_data)
+    session.add(db_user)
+    session.commit()
+    session.refresh(db_user)
+    return db_user
+
+
+def get_user_by_email(*, session: Session, email: str) -> User | None:
+    statement = select(User).where(User.email == email)
+    session_user = session.exec(statement).first()
+    return session_user
+
+
+# Dummy hash to use for timing attack prevention when user is not found
+# This is an Argon2 hash of a random password, used to ensure constant-time comparison
+DUMMY_HASH = "$argon2id$v=19$m=65536,t=3,p=4$MjQyZWE1MzBjYjJlZTI0Yw$YTU4NGM5ZTZmYjE2NzZlZjY0ZWY3ZGRkY2U2OWFjNjk"
+
+
+def authenticate(*, session: Session, email: str, password: str) -> User | None:
+    db_user = get_user_by_email(session=session, email=email)
+    if not db_user:
+        # Prevent timing attacks by running password verification even when user doesn't exist
+        # This ensures the response time is similar whether or not the email exists
+        verify_password(password, DUMMY_HASH)
+        return None
+    verified, updated_password_hash = verify_password(password, db_user.hashed_password)
+    if not verified:
+        return None
+    if updated_password_hash:
+        db_user.hashed_password = updated_password_hash
+        session.add(db_user)
+        session.commit()
+        session.refresh(db_user)
+    return db_user