refactor: Represent route auth information in the type system

src/api/client/capabilities.rs

@@ -48,11 +48,7 @@ pub(crate) async fn get_capabilities_route(
 		json!({"enabled": services.config.forget_forced_upon_leave}),
 	)?;
 
-	if services
-		.users
-		.is_admin(body.sender_user.as_ref().unwrap())
-		.await
-	{
+	if services.users.is_admin(body.identity.sender_user()).await {
 		// Advertise suspension API
 		capabilities.set("uk.timedout.msc4323", json!({"suspend": true, "lock": false}))?;
 	}