curl "https://app.tatango.com/api/v2/lists/<ID>/custom_fields" -X GET \
  -H "Accept: application/json" \
  -H "Content-Type: application/json" \
  -u emailaddress@mydomain.com:my_api_key \
  -H "Host: example.org" \
  -H "Cookie: "

{
  "status": "OK",
  "custom_fields": [
    {
      "key": "some_custom_field_name",
      "pattern": "[A-Za-z0-9]",
      "max_length": 9999,
      "default_value": "The Default Value",
      "label": "The Label",
      "content_type": "text",
      "should_validate_regex_via_api": false
    }
  ]
}