You can add your own custom json-serializable metadata to pulls by specifying custom query parameters on your Canopy Connect link. Custom query parameters use the format:
ccmeta-YOUR_CUSTOM_ATTRIBUTE=YOUR_CUSTOM_VALUE
For example, adding:
?ccmeta-user_id=5&ccmeta-referrer=John
will add the following metadata to your pull's meta_data field when you retrieve it from the api endpoint:
{
"user_id": "5",
"referrer": "John"
}