diff --git a/src/api/client_server/membership.rs b/src/api/client_server/membership.rs
index a0426143..9eb28717 100644
--- a/src/api/client_server/membership.rs
+++ b/src/api/client_server/membership.rs
@@ -2,6 +2,7 @@ use ruma::{
     api::{
         client::{
             error::ErrorKind,
+            knock::{self, knock_room},
             membership::{
                 ban_user, forget_room, get_member_events, invite_user, join_room_by_id,
                 join_room_by_id_or_alias, joined_members, joined_rooms, kick_user, leave_room,
@@ -140,6 +141,53 @@ pub async fn join_room_by_id_or_alias_route(
     })
 }
 
+/// # `POST /_matrix/client/r0/join/{roomIdOrAlias}`
+///
+/// Tries to knock the room to ask permission to join for the sender user.
+pub async fn knock_room_route(
+    body: Ruma<knock_room::v3::Request>,
+) -> Result<knock_room::v3::Response> {
+    let sender_user = body.sender_user.as_deref().expect("user is authenticated");
+    let body = body.body;
+
+    let (servers, room_id) = match OwnedRoomId::try_from(body.room_id_or_alias) {
+        Ok(room_id) => {
+            let mut servers = body.server_name.clone();
+            servers.extend(
+                services()
+                    .rooms
+                    .state_cache
+                    .invite_state(sender_user, &room_id)?
+                    .unwrap_or_default()
+                    .iter()
+                    .filter_map(|event| serde_json::from_str(event.json().get()).ok())
+                    .filter_map(|event: serde_json::Value| event.get("sender").cloned())
+                    .filter_map(|sender| sender.as_str().map(|s| s.to_owned()))
+                    .filter_map(|sender| UserId::parse(sender).ok())
+                    .map(|user| user.server_name().to_owned()),
+            );
+
+            servers.push(
+                room_id
+                    .server_name()
+                    .expect("Room IDs should always have a server name")
+                    .into(),
+            );
+
+            (servers, room_id)
+        }
+        Err(room_alias) => {
+            let response = get_alias_helper(room_alias).await?;
+
+            (response.servers, response.room_id)
+        }
+    };
+
+    Ok(knock_room_by_id_or_alias::v3::Response {
+        room_id: knock_room_response.room_id,
+    })
+}
+
 /// # `POST /_matrix/client/r0/rooms/{roomId}/leave`
 ///
 /// Tries to leave the sender user from a room.