Plugins » Katello

                        "apis": [
                            {
                                "api_url": "/katello/api/organizations/:organization_id/subscriptions/upload",
                                "deprecated": null,
                                "http_method": "POST",
                                "short_description": "Upload a subscription manifest" 
                            }
                        ],
                        "params": [
                            {
                                "allow_blank": false,
                                "allow_nil": false,
                                "description": "\n<p>Subscription manifest file</p>\n",
                                "expected_type": "string",
                                "full_name": "content",
                                "metadata": null,
                                "name": "content",
                                "required": true,
                                "show": true,
                                "validations": [],
                                "validator": "File" 
                            },
…

I think saying that the file should be a string is quite far fetched :)