Equalize Access login failure handling

src/govoplan_access/backend/api/v1/auth.py

@@ -50,7 +50,7 @@ from govoplan_core.settings import settings
 from govoplan_access.backend.semantic import collect_function_assignment_ids, collect_function_delegation_ids, identity_id_for_account
 from govoplan_access.backend.auth.tenant_context import AccessTenantContextSwitcher
 from govoplan_access.backend.security.api_keys import authenticate_api_key
-from govoplan_access.backend.security.passwords import verify_password
+from govoplan_access.backend.security.passwords import DUMMY_PASSWORD_HASH, verify_password
 from govoplan_access.backend.security.sessions import (
     authenticate_session_token,
     collect_user_authorization_context,
@@ -253,7 +253,9 @@ def _resolve_login_user(session: Session, payload: LoginRequest) -> tuple[Accoun
         .filter(Account.normalized_email == normalize_email(payload.email), Account.is_active.is_(True))
         .one_or_none()
     )
-    if account is None or not verify_password(payload.password, account.password_hash):
+    password_hash = account.password_hash if account is not None and account.password_hash else DUMMY_PASSWORD_HASH
+    password_matches = verify_password(payload.password, password_hash)
+    if account is None or not account.password_hash or not password_matches:
         raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid login")
 
     query = (
@@ -269,7 +271,9 @@ def _resolve_login_user(session: Session, payload: LoginRequest) -> tuple[Accoun
         query = query.filter(Tenant.slug == payload.tenant_slug)
     row = query.order_by(Tenant.name.asc()).first()
     if row is None:
-        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="No active tenant membership")
+        # Keep every authentication failure generic so callers cannot infer
+        # whether an account exists but lacks an active tenant membership.
+        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid login")
     return account, row[0], row[1]
 
 

src/govoplan_access/backend/security/passwords.py

@@ -9,6 +9,14 @@ _ALGORITHM = "pbkdf2_sha256"
 _DEFAULT_ITERATIONS = 260_000
 _SALT_BYTES = 16
 
+# A valid, fixed-cost hash used when a login identity has no local password hash.
+# Its plaintext value is intentionally irrelevant; the hash only keeps failed
+# login attempts on the same verification path as existing local accounts.
+DUMMY_PASSWORD_HASH = (
+    "pbkdf2_sha256$260000$Z292b3BsYW4tZHVtbXktdjE="  # noqa: S105  # nosec B105 - non-account timing equalizer.
+    "$uWgE7ht8wO6cotOqNKK2yNomPt57gstVss5ben5gTbw="
+)
+
 
 def hash_password(password: str, *, iterations: int = _DEFAULT_ITERATIONS) -> str:
     salt = os.urandom(_SALT_BYTES)
@@ -37,4 +45,3 @@ def verify_password(password: str, encoded: str | None) -> bool:
         return False
     actual = hashlib.pbkdf2_hmac("sha256", password.encode("utf-8"), salt, iterations)
     return hmac.compare_digest(actual, expected)
-