assets/manifest.json

{
  "name" : "External Provider",
  "desc" : "Buy content from an external provider",
  "embed" : [{
    "panel" : "match",
    "title" : "Buy",
    "classes" : ["cart"],
    "onClick" : {
      "action" : "addWidget",
      "template" : "https://korap.ids-mannheim.de/instance/test/plugin/external/",
      "permissions": [
        "scripts",
        "popups" 
      ]
    }
  }]
}