(amd64)ubuntu@localhost:~$ sudo http.do PUT snapd:///1.0/packages '{"basic-config.sideload": "key: value"}'
HTTP/1.1 400 Bad Request
Content-Length: 151
Content-Type: application/json
Date: Tue, 01 Dec 2015 14:23:24 GMT

{
    "result": {
        "msg": "can't decode request body into map[string]string: EOF",
        "obj": {},
        "str": "EOF"
    },
    "status": "Bad Request",
    "status_code": 400,
    "type": "error"
}