feat: add PasswordService with argon2 hash/verify

src/fastapi_oidc_op/authn/password.py

@@ -0,0 +1,20 @@
+from argon2 import PasswordHasher
+from argon2.exceptions import InvalidHashError, VerifyMismatchError
+
+
+class PasswordService:
+    """Argon2 password hashing and verification."""
+
+    def __init__(self, hasher: PasswordHasher | None = None) -> None:
+        self._hasher = hasher or PasswordHasher()
+
+    def hash(self, password: str) -> str:
+        """Hash a password using argon2id. Returns the full hash string."""
+        return self._hasher.hash(password)
+
+    def verify(self, password_hash: str, password: str) -> bool:
+        """Verify a password against an argon2 hash. Returns True if valid."""
+        try:
+            return self._hasher.verify(password_hash, password)
+        except (VerifyMismatchError, InvalidHashError):
+            return False