FIX GCG: forward hf_token as None instead of an empty string (#2275)

Co-authored-by: Roman Lutz <romanlutz13@gmail.com>

Author: immu4989

pyrit/executor/promptgen/gcg/attack/base/attack_manager.py

@@ -1819,7 +1819,7 @@ class ModelWorker:
     def __init__(
         self,
         model_path: str,
-        token: str,
+        token: str | None,
         model_kwargs: dict[str, Any],
         tokenizer: Any,
         device: str,

pyrit/executor/promptgen/gcg/generator.py

@@ -410,7 +410,10 @@ def _to_attack_params(self, *, context: GCGContext) -> Any:
 
         all_models = self._models + self._test_models
         return SimpleNamespace(
-            token=self._hf_token or "",
+            # None means anonymous access. An empty string makes huggingface_hub send
+            # "Authorization: Bearer " with no credential, which httpx rejects as an
+            # illegal header value, so public models would fail to load.
+            token=self._hf_token,
             tokenizer_paths=[m.name for m in all_models],
             tokenizer_kwargs=[m.tokenizer_kwargs for m in all_models],
             model_paths=[m.name for m in all_models],

tests/unit/executor/promptgen/gcg/test_generator.py

@@ -158,6 +158,27 @@ def test_test_length_mismatch_raises(self) -> None:
             )
 
 
+class TestToAttackParamsToken:
+    """The HuggingFace token forwarded to model loading."""
+
+    def test_token_is_none_when_not_supplied(self) -> None:
+        # An empty string makes huggingface_hub send "Authorization: Bearer " with no
+        # credential, which httpx rejects as an illegal header value. None means anonymous,
+        # which is what loading a public model needs.
+        gen = GCGGenerator(models=[GCGModelConfig(name=_LLAMA_2)])
+
+        params = gen._to_attack_params(context=GCGContext(goals=["g"], targets=["t"]))
+
+        assert params.token is None
+
+    def test_token_is_forwarded_when_supplied(self) -> None:
+        gen = GCGGenerator(models=[GCGModelConfig(name=_LLAMA_2)], hf_token="hf_example")
+
+        params = gen._to_attack_params(context=GCGContext(goals=["g"], targets=["t"]))
+
+        assert params.token == "hf_example"
+
+
 @pytest.fixture
 def patched_get_workers():
     """Patch the heavy worker spawn so lifecycle tests don't try to load real models."""