Fix IndexError in Digest auth header parser on empty values

src/httpx2/httpx2/_auth.py

@@ -10,7 +10,7 @@
 
 from ._exceptions import ProtocolError
 from ._models import Cookies, Request, Response
-from ._utils import to_bytes, to_str, unquote
+from ._utils import to_bytes, to_str
 
 if typing.TYPE_CHECKING:
     from hashlib import _Hash
@@ -225,7 +225,7 @@ def _parse_challenge(self, request: Request, response: Response, auth_header: st
         header_dict: dict[str, str] = {}
         for field in parse_http_list(fields):
             key, value = field.strip().split("=", 1)
-            header_dict[key] = unquote(value)
+            header_dict[key] = value.strip('"')
 
         try:
             realm = header_dict["realm"].encode()

src/httpx2/httpx2/_utils.py

@@ -86,10 +86,6 @@ def to_bytes_or_str(value: str, match_type_of: typing.AnyStr) -> typing.AnyStr:
     return value if isinstance(match_type_of, str) else value.encode()
 
 
-def unquote(value: str) -> str:
-    return value[1:-1] if value[0] == value[-1] == '"' else value
-
-
 def peek_filelike_length(stream: typing.Any) -> int | None:
     """
     Given a file-like stream object, return its length in number of bytes

tests/httpx2/test_auth.py

@@ -258,3 +258,18 @@ def mock_get_client_nonce(nonce_count: int, nonce: bytes) -> bytes:
     response = httpx2.Response(content=b"Hello, world!", status_code=200)
     with pytest.raises(StopIteration):
         flow.send(response)
+
+
+def test_digest_auth_empty_realm() -> None:
+    auth = httpx2.DigestAuth(username="user", password="pass")
+    request = httpx2.Request("GET", "https://www.example.com")
+
+    flow = auth.sync_auth_flow(request)
+    request = next(flow)
+
+    # Digest realm has been left empty.
+    headers = {"WWW-Authenticate": 'Digest realm=, qop="auth", nonce="...", opaque="..."'}
+    response = httpx2.Response(content=b"Auth required", status_code=401, headers=headers, request=request)
+    request = flow.send(response)
+
+    assert request.headers["Authorization"].startswith('Digest username="user", realm="", nonce="..."')