In GatedContent.com it is possible to configure gate editor fields.
For example let's say you wanted to allow marketers building gates to add a Campaign ID to the metadata passed on submission.
First create a new hidden field called Campaign_ID and select the Gate Editor option from the prepopulation dropdown.
You can then configure this field with a type, label hint and mandatory status. You can also determine which form types this field will be available for.
Once this has been configured, return to the gate editor and run a quick submission test to make sure the data is being received properly.