diff --git a/changelog.d/12304.misc b/changelog.d/12304.misc
new file mode 100644
index 000000000000..88fd6b92ee4f
--- /dev/null
+++ b/changelog.d/12304.misc
@@ -0,0 +1 @@
+Refactor `create_new_client_event` to use a new parameter, `state_event_ids`, which accurately describes the usage with [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) instead of abusing `auth_event_ids`.
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 1c4fb4360af9..766f597a55bd 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -782,7 +782,6 @@ async def create_and_send_nonmember_event(
         event_dict: dict,
         allow_no_prev_events: bool = False,
         prev_event_ids: Optional[List[str]] = None,
-        auth_event_ids: Optional[List[str]] = None,
         state_event_ids: Optional[List[str]] = None,
         ratelimit: bool = True,
         txn_id: Optional[str] = None,
@@ -807,12 +806,6 @@ async def create_and_send_nonmember_event(
                 The event IDs to use as the prev events.
                 Should normally be left as None to automatically request them
                 from the database.
-            auth_event_ids:
-                The event ids to use as the auth_events for the new event.
-                Should normally be left as None, which will cause them to be calculated
-                based on the room state at the prev_events.
-
-                If non-None, prev_event_ids must also be provided.
             state_event_ids:
                 The full state at a given event. This is used particularly by the MSC2716
                 /batch_send endpoint. One use case is with insertion events which float at
@@ -878,7 +871,6 @@ async def create_and_send_nonmember_event(
                 txn_id=txn_id,
                 allow_no_prev_events=allow_no_prev_events,
                 prev_event_ids=prev_event_ids,
-                auth_event_ids=auth_event_ids,
                 state_event_ids=state_event_ids,
                 outlier=outlier,
                 historical=historical,
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index a33fa34aa8df..0785e3111417 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -271,7 +271,6 @@ async def _local_membership_update(
         membership: str,
         allow_no_prev_events: bool = False,
         prev_event_ids: Optional[List[str]] = None,
-        auth_event_ids: Optional[List[str]] = None,
         state_event_ids: Optional[List[str]] = None,
         txn_id: Optional[str] = None,
         ratelimit: bool = True,
@@ -295,10 +294,6 @@ async def _local_membership_update(
                 events should have a prev_event and we should only use this in special
                 cases like MSC2716.
             prev_event_ids: The event IDs to use as the prev events
-            auth_event_ids:
-                The event ids to use as the auth_events for the new event.
-                Should normally be left as None, which will cause them to be calculated
-                based on the room state at the prev_events.
             state_event_ids:
                 The full state at a given event. This is used particularly by the MSC2716
                 /batch_send endpoint. One use case is the historical `state_events_at_start`;
@@ -361,7 +356,6 @@ async def _local_membership_update(
             txn_id=txn_id,
             allow_no_prev_events=allow_no_prev_events,
             prev_event_ids=prev_event_ids,
-            auth_event_ids=auth_event_ids,
             state_event_ids=state_event_ids,
             require_consent=require_consent,
             outlier=outlier,
@@ -465,7 +459,6 @@ async def update_membership(
         historical: bool = False,
         allow_no_prev_events: bool = False,
         prev_event_ids: Optional[List[str]] = None,
-        auth_event_ids: Optional[List[str]] = None,
         state_event_ids: Optional[List[str]] = None,
     ) -> Tuple[str, int]:
         """Update a user's membership in a room.
@@ -494,10 +487,6 @@ async def update_membership(
                 events should have a prev_event and we should only use this in special
                 cases like MSC2716.
             prev_event_ids: The event IDs to use as the prev events
-            auth_event_ids:
-                The event ids to use as the auth_events for the new event.
-                Should normally be left as None, which will cause them to be calculated
-                based on the room state at the prev_events.
             state_event_ids:
                 The full state at a given event. This is used particularly by the MSC2716
                 /batch_send endpoint. One use case is the historical `state_events_at_start`;
@@ -544,7 +533,6 @@ async def update_membership(
                     historical=historical,
                     allow_no_prev_events=allow_no_prev_events,
                     prev_event_ids=prev_event_ids,
-                    auth_event_ids=auth_event_ids,
                     state_event_ids=state_event_ids,
                 )
 
@@ -567,7 +555,6 @@ async def update_membership_locked(
         historical: bool = False,
         allow_no_prev_events: bool = False,
         prev_event_ids: Optional[List[str]] = None,
-        auth_event_ids: Optional[List[str]] = None,
         state_event_ids: Optional[List[str]] = None,
     ) -> Tuple[str, int]:
         """Helper for update_membership.
@@ -598,10 +585,6 @@ async def update_membership_locked(
                 events should have a prev_event and we should only use this in special
                 cases like MSC2716.
             prev_event_ids: The event IDs to use as the prev events
-            auth_event_ids:
-                The event ids to use as the auth_events for the new event.
-                Should normally be left as None, which will cause them to be calculated
-                based on the room state at the prev_events.
             state_event_ids:
                 The full state at a given event. This is used particularly by the MSC2716
                 /batch_send endpoint. One use case is the historical `state_events_at_start`;
@@ -736,7 +719,6 @@ async def update_membership_locked(
                 ratelimit=ratelimit,
                 allow_no_prev_events=allow_no_prev_events,
                 prev_event_ids=prev_event_ids,
-                auth_event_ids=auth_event_ids,
                 state_event_ids=state_event_ids,
                 content=content,
                 require_consent=require_consent,
@@ -961,7 +943,6 @@ async def update_membership_locked(
             txn_id=txn_id,
             ratelimit=ratelimit,
             prev_event_ids=latest_event_ids,
-            auth_event_ids=auth_event_ids,
             state_event_ids=state_event_ids,
             content=content,
             require_consent=require_consent,