fix(vector_stores): name the connection string when Atlas rejects MongoDB credentials

Atlas answers a wrong password with code 8000 "AtlasError" rather than the 18 a
self-hosted deployment returns, so the code-only check never fired and a bad
password came back as a generic "MongoDB rejected the vector search", pointing
the reader at the index instead of at their credentials. Verified live against
Atlas with a tampered password.

litellm/llms/mongodb/common_utils.py

@@ -110,6 +110,9 @@ def reset_client_cache() -> None:
 
 _AUTHENTICATION_FAILED_CODE: Final = 18
 _UNAUTHORIZED_CODE: Final = 13
+# Atlas reports a rejected user as code 8000 "AtlasError" rather than 18, so the
+# message is the only reliable signal for a serverless or shared-tier deployment.
+_AUTHENTICATION_MESSAGE_MARKERS: Final = ("bad auth", "authentication failed", "not authorized")
 
 
 def _index_hint(index_name: str, database: str, collection: str) -> str:
@@ -169,12 +172,14 @@ def translate_mongo_error(error: Exception, index_name: str, database: str, coll
         )
     if isinstance(error, OperationFailure):
         code: Final = error.code
-        if code in (_AUTHENTICATION_FAILED_CODE, _UNAUTHORIZED_CODE):
+        detail: Final = str(error).lower()
+        if code in (_AUTHENTICATION_FAILED_CODE, _UNAUTHORIZED_CODE) or any(
+            marker in detail for marker in _AUTHENTICATION_MESSAGE_MARKERS
+        ):
             return config_error(
                 "MongoDB rejected the credentials in mongodb_connection_string, or the database user "
                 f"lacks read access to '{database}.{collection}'. Driver detail: {error.details}"
             )
-        detail: Final = str(error).lower()
         if "dimension" in detail:
             return config_error(
                 "The query embedding does not match the vector dimensions the Atlas index was built for. "

tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py

@@ -860,3 +860,30 @@ class TestErrorsCarryTheRightHttpStatus:
             translate_mongo_error(original, index_name="idx", database="db", collection="coll")
             is original
         )
+
+
+def test_atlas_rejected_credentials_are_named_even_though_the_code_is_8000():
+    """Atlas answers a wrong password with code 8000 "AtlasError", not the 18 that a
+    self-hosted deployment returns, so a code-only check reports it as a generic
+    rejected search and never tells the caller to look at their connection string."""
+    from pymongo.errors import OperationFailure
+
+    error = OperationFailure(
+        "bad auth : authentication failed",
+        code=8000,
+        details={"ok": 0, "errmsg": "bad auth : authentication failed", "code": 8000, "codeName": "AtlasError"},
+    )
+    translated = translate_mongo_error(error, index_name="idx", database="sample_mflix", collection="embedded_movies")
+
+    assert isinstance(translated, BadRequestError)
+    assert "mongodb_connection_string" in str(translated)
+    assert "sample_mflix.embedded_movies" in str(translated)
+
+
+def test_a_rejected_search_that_is_not_an_auth_failure_keeps_the_generic_message():
+    from pymongo.errors import OperationFailure
+
+    error = OperationFailure("PlanExecutor error", code=8, details={"errmsg": "PlanExecutor error"})
+    translated = translate_mongo_error(error, index_name="idx", database="db", collection="coll")
+
+    assert "mongodb_connection_string" not in str(translated)