fix(database): reject non-dict encrypted_extra at schema validation layer

encrypted_extra_validator only checked that the value was valid JSON but
did not verify the decoded value was a dict.  Non-dict JSON values
(int, null, list, bool, bare string) passed validation and later caused
an AttributeError in _handle_oauth2() when .get() was called on a
non-mapping, surfacing as an opaque 500 instead of a 422.

Add an isinstance(…, dict) guard mirroring the identical fix already
applied to extra_validator in #44092.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

superset/databases/schemas.py

@@ -245,12 +245,22 @@ def encrypted_extra_validator(value: str | None) -> None:
     """
     if value:
         try:
-            json.loads(value)
+            encrypted_extra = json.loads(value)
         except json.JSONDecodeError as ex:
             raise ValidationError(
                 [_("Field cannot be decoded by JSON. %(msg)s", msg=str(ex))]
             ) from ex
 
+        if not isinstance(encrypted_extra, dict):
+            raise ValidationError(
+                [
+                    _(
+                        "Encrypted extra field must be a mapping"
+                        " from string keys to values."
+                    )
+                ]
+            )
+
 
 def masked_encrypted_extra_validator(value: str) -> None:
     """

tests/unit_tests/databases/schema_tests.py

@@ -614,6 +614,27 @@ def test_extra_validator_rejects_non_dict_top_level_value(value: Any) -> None:
     assert "must be a mapping" in str(exc_info.value)
 
 
+@pytest.mark.parametrize("value", [123, None, [1, 2], True, "abc"])
+def test_encrypted_extra_validator_rejects_non_dict_top_level_value(
+    value: Any,
+) -> None:
+    """
+    Test that encrypted_extra_validator rejects a top-level value that is valid
+    JSON but not a mapping (int, null, list, bool, string), instead of letting
+    AttributeError propagate from downstream .get() calls.
+    """
+    from superset.databases.schemas import DatabasePostSchema
+
+    schema = DatabasePostSchema()
+    payload = {
+        "database_name": "test_db",
+        "masked_encrypted_extra": json.dumps(value),
+    }
+    with pytest.raises(ValidationError) as exc_info:
+        schema.load(payload)
+    assert "must be a mapping" in str(exc_info.value)
+
+
 def test_cache_timeout_rejects_values_below_minus_one() -> None:
     """
     Test that cache_timeout rejects values less than -1.