diff --git a/backend/src/cyclone/auth/__init__.py b/backend/src/cyclone/auth/__init__.py
new file mode 100644
index 0000000..31402c2
--- /dev/null
+++ b/backend/src/cyclone/auth/__init__.py
@@ -0,0 +1 @@
+"""Auth module — users, sessions, permissions, routes, admin, rate_limit."""
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diff --git a/backend/src/cyclone/auth/users.py b/backend/src/cyclone/auth/users.py
new file mode 100644
index 0000000..3107bcd
--- /dev/null
+++ b/backend/src/cyclone/auth/users.py
@@ -0,0 +1,79 @@
+"""User CRUD + bcrypt password hashing."""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from typing import Any
+
+from passlib.hash import bcrypt
+from sqlalchemy import select
+
+from cyclone.db import User
+
+
+def hash_password(plaintext: str) -> str:
+    return bcrypt.hash(plaintext)
+
+
+def verify_password(plaintext: str, hashed: str) -> bool:
+    try:
+        return bcrypt.verify(plaintext, hashed)
+    except (ValueError, TypeError):
+        return False
+
+
+def create(db, *, username: str, password: str, role: str) -> User:
+    user = User(
+        username=username,
+        password_hash=hash_password(password),
+        role=role,
+        created_at=datetime.now(timezone.utc),
+    )
+    db.add(user)
+    db.commit()
+    db.refresh(user)
+    return user
+
+
+def get_by_username(db, username: str) -> User | None:
+    return db.execute(
+        select(User).where(User.username == username)
+    ).scalar_one_or_none()
+
+
+def get(db, user_id: int) -> User | None:
+    return db.get(User, user_id)
+
+
+def disable(db, user_id: int) -> None:
+    user = db.get(User, user_id)
+    if user is None:
+        return
+    user.disabled_at = datetime.now(timezone.utc)
+    db.commit()
+
+
+def update_role(db, user_id: int, role: str) -> None:
+    user = db.get(User, user_id)
+    if user is None:
+        return
+    user.role = role
+    db.commit()
+
+
+def update_password(db, user_id: int, new_password: str) -> None:
+    user = db.get(User, user_id)
+    if user is None:
+        return
+    user.password_hash = hash_password(new_password)
+    db.commit()
+
+
+def to_public(user: User) -> dict[str, Any]:
+    return {
+        "id": user.id,
+        "username": user.username,
+        "role": user.role,
+        "createdAt": user.created_at.isoformat() if user.created_at else None,
+        "disabledAt": user.disabled_at.isoformat() if user.disabled_at else None,
+    }
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diff --git a/backend/tests/test_auth_users.py b/backend/tests/test_auth_users.py
new file mode 100644
index 0000000..b6ce096
--- /dev/null
+++ b/backend/tests/test_auth_users.py
@@ -0,0 +1,93 @@
+"""Unit tests for cyclone.auth.users — User CRUD + bcrypt hashing."""
+
+from __future__ import annotations
+
+import pytest
+from sqlalchemy import delete
+
+from cyclone.auth import users
+from cyclone.db import SessionLocal, User
+
+
+@pytest.fixture(autouse=True)
+def _clear_users():
+    with SessionLocal()() as db:
+        db.execute(delete(User))
+        db.commit()
+    yield
+    with SessionLocal()() as db:
+        db.execute(delete(User))
+        db.commit()
+
+
+def test_hash_password_returns_bcrypt():
+    h = users.hash_password("hunter2hunter2")
+    assert h.startswith("$2")
+
+
+def test_hash_password_produces_unique_salts():
+    a = users.hash_password("same-password")
+    b = users.hash_password("same-password")
+    assert a != b
+
+
+def test_verify_password_correct():
+    h = users.hash_password("hunter2hunter2")
+    assert users.verify_password("hunter2hunter2", h) is True
+
+
+def test_verify_password_incorrect():
+    h = users.hash_password("hunter2hunter2")
+    assert users.verify_password("WRONG", h) is False
+
+
+def test_create_user_persists_with_hashed_password():
+    with SessionLocal()() as db:
+        u = users.create(db, username="alice", password="hunter2hunter2", role="admin")
+    assert u.id is not None
+    assert u.username == "alice"
+    assert u.role == "admin"
+    assert u.disabled_at is None
+    assert u.password_hash != "hunter2hunter2"
+    assert u.password_hash.startswith("$2")
+
+
+def test_create_user_rejects_duplicate_username():
+    with SessionLocal()() as db:
+        users.create(db, username="bob", password="hunter2hunter2", role="user")
+    with SessionLocal()() as db:
+        with pytest.raises(Exception):
+            users.create(db, username="bob", password="anotherone", role="user")
+
+
+def test_get_by_username_returns_user():
+    with SessionLocal()() as db:
+        users.create(db, username="carol", password="hunter2hunter2", role="viewer")
+    with SessionLocal()() as db:
+        u = users.get_by_username(db, "carol")
+    assert u is not None
+    assert u.username == "carol"
+
+
+def test_get_by_username_returns_none_for_missing():
+    with SessionLocal()() as db:
+        assert users.get_by_username(db, "ghost") is None
+
+
+def test_disable_user_sets_disabled_at():
+    with SessionLocal()() as db:
+        u = users.create(db, username="dave", password="hunter2hunter2", role="user")
+        users.disable(db, u.id)
+    with SessionLocal()() as db:
+        refreshed = users.get_by_username(db, "dave")
+    assert refreshed.disabled_at is not None
+
+
+def test_to_public_shape_omits_password_hash():
+    with SessionLocal()() as db:
+        u = users.create(db, username="eve", password="hunter2hunter2", role="admin")
+        shape = users.to_public(u)
+    assert "password_hash" not in shape
+    assert shape["username"] == "eve"
+    assert shape["role"] == "admin"
+    assert "id" in shape and "createdAt" in shape
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