Hash passwords with PBKDF2-SHA256 instead of storing plaintext

Existing plaintext passwords are auto-upgraded to hashed on next login.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/main.py

@@ -6,9 +6,35 @@ import json
 import os
 
 from backend.database import get_db, init_db, seed_defaults, log_audit
+import hashlib
+import secrets as _secrets
 
 app = FastAPI(title="Essential Oil Formula Calculator API")
 
+
+# ── Password hashing (PBKDF2-SHA256, stdlib) ─────────
+def hash_password(password: str) -> str:
+    salt = _secrets.token_hex(16)
+    h = hashlib.pbkdf2_hmac("sha256", password.encode(), salt.encode(), 200_000)
+    return f"{salt}${h.hex()}"
+
+
+def verify_password(password: str, stored: str) -> bool:
+    if not stored:
+        return False
+    if "$" not in stored:
+        # Legacy plaintext — compare directly
+        return password == stored
+    salt, h = stored.split("$", 1)
+    return hashlib.pbkdf2_hmac("sha256", password.encode(), salt.encode(), 200_000).hex() == h
+
+
+def _upgrade_password_if_needed(conn, user_id: int, password: str, stored: str):
+    """If stored password is legacy plaintext, upgrade to hashed."""
+    if stored and "$" not in stored:
+        conn.execute("UPDATE users SET password = ? WHERE id = ?", (hash_password(password), user_id))
+        conn.commit()
+
 # Periodic WAL checkpoint to ensure data is flushed to main DB file
 import threading, time as _time
 def _wal_checkpoint_loop():
@@ -312,7 +338,6 @@ def symptom_search(body: dict, user=Depends(get_current_user)):
 # ── Register ────────────────────────────────────────────
 @app.post("/api/register", status_code=201)
 def register(body: dict):
-    import secrets
     username = body.get("username", "").strip()
     password = body.get("password", "").strip()
     display_name = body.get("display_name", "").strip()
@@ -320,12 +345,12 @@ def register(body: dict):
         raise HTTPException(400, "用户名至少2个字符")
     if not password or len(password) < 4:
         raise HTTPException(400, "密码至少4位")
-    token = secrets.token_hex(24)
+    token = _secrets.token_hex(24)
     conn = get_db()
     try:
         conn.execute(
             "INSERT INTO users (username, token, role, display_name, password) VALUES (?, ?, ?, ?, ?)",
-            (username, token, "viewer", display_name or username, password)
+            (username, token, "viewer", display_name or username, hash_password(password))
         )
         conn.commit()
     except Exception:
@@ -343,14 +368,19 @@ def login(body: dict):
     if not username or not password:
         raise HTTPException(400, "请输入用户名和密码")
     conn = get_db()
-    user = conn.execute("SELECT token, password, display_name, role FROM users WHERE username = ?", (username,)).fetchone()
-    conn.close()
+    user = conn.execute("SELECT id, token, password, display_name, role FROM users WHERE username = ?", (username,)).fetchone()
     if not user:
+        conn.close()
         raise HTTPException(401, "用户名不存在")
     if not user["password"]:
+        conn.close()
         raise HTTPException(401, "该账号未设置密码，请使用链接登录后设置密码")
-    if user["password"] != password:
+    if not verify_password(password, user["password"]):
+        conn.close()
         raise HTTPException(401, "密码错误")
+    # Auto-upgrade legacy plaintext password to hashed
+    _upgrade_password_if_needed(conn, user["id"], password, user["password"])
+    conn.close()
     return {"token": user["token"], "display_name": user["display_name"], "role": user["role"]}
 
 
@@ -385,11 +415,11 @@ def update_me(body: dict, user=Depends(get_current_user)):
             raise HTTPException(400, "新密码至少4位")
         old_pw = body.get("old_password", "").strip()
         current_pw = user.get("password") or ""
-        if current_pw and old_pw != current_pw:
+        if current_pw and not verify_password(old_pw, current_pw):
             conn.close()
             raise HTTPException(400, "当前密码不正确")
         if pw:
-            conn.execute("UPDATE users SET password = ? WHERE id = ?", (pw, user["id"]))
+            conn.execute("UPDATE users SET password = ? WHERE id = ?", (hash_password(pw), user["id"]))
     conn.commit()
     conn.close()
     return {"ok": True}
@@ -404,7 +434,7 @@ def set_password(body: dict, user=Depends(get_current_user)):
     if not pw or len(pw) < 4:
         raise HTTPException(400, "密码至少4位")
     conn = get_db()
-    conn.execute("UPDATE users SET password = ? WHERE id = ?", (pw, user["id"]))
+    conn.execute("UPDATE users SET password = ? WHERE id = ?", (hash_password(pw), user["id"]))
     conn.commit()
     conn.close()
     return {"ok": True}
@@ -896,8 +926,7 @@ def list_users(user=Depends(require_role("admin"))):
 
 @app.post("/api/users", status_code=201)
 def create_user(body: UserIn, user=Depends(require_role("admin"))):
-    import secrets
-    token = secrets.token_hex(24)
+    token = _secrets.token_hex(24)
     conn = get_db()
     try:
         conn.execute(