Imports to top of file (ruff rule now). Refactor a couple of import cycles by implementing clear hierarchy of modules.

cista/util/pwhash.py

@@ -0,0 +1,47 @@
+import hmac
+import re
+from typing import Protocol
+from unicodedata import normalize
+
+import argon2
+
+_argon = argon2.PasswordHasher()
+_droppyhash = re.compile(r"^([a-f0-9]{64})\$([a-f0-9]{8})$")
+
+
+class SupportsHash(Protocol):
+    hash: str
+
+
+def normalize_secret(value: str) -> bytes:
+    return normalize("NFC", value).strip().encode()
+
+
+def verify_hash(user_hash: str, *, username: str, password: str) -> bool:
+    """Verify password hash and return whether the stored hash should be upgraded."""
+    if not user_hash:
+        raise ValueError("Account disabled")
+
+    normalized_username = normalize_secret(username)
+    normalized_password = normalize_secret(password)
+
+    if (match := _droppyhash.match(user_hash)) is not None:
+        expected_hash, salt = match.groups()
+        computed_hash = hmac.digest(
+            normalized_password + salt.encode() + normalized_username,
+            b"",
+            "sha256",
+        ).hex()
+        if not hmac.compare_digest(expected_hash, computed_hash):
+            raise ValueError("Invalid password")
+        return True
+
+    try:
+        _argon.verify(user_hash, normalized_password)
+    except Exception:
+        raise ValueError("Invalid password") from None
+    return _argon.check_needs_rehash(user_hash)
+
+
+def set_password(user: SupportsHash, password: str) -> None:
+    user.hash = _argon.hash(normalize_secret(password))