Improve federated ID validation (#8372)

* Fix URI not being sufficiently validated with prefetched JSON

* Add additional id validation to OStatus documents, when possible

app/lib/ostatus/activity/creation.rb

@@ -7,7 +7,7 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
       return [nil, false]
     end
 
-    return [nil, false] if @account.suspended?
+    return [nil, false] if @account.suspended? || invalid_origin?
 
     RedisLock.acquire(lock_options) do |lock|
       if lock.acquired?
@@ -204,6 +204,15 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
     end
   end
 
+  def invalid_origin?
+    return false unless id.start_with?('http') # Legacy IDs cannot be checked
+
+    needle = Addressable::URI.parse(id).normalized_host
+
+    !(needle.casecmp(@account.domain).zero? ||
+      needle.casecmp(Addressable::URI.parse(@account.remote_url.presence || @account.uri).normalized_host).zero?)
+  end
+
   def lock_options
     { redis: Redis.current, key: "create:#{id}" }
   end