curl 'https://www.googleapis.com/urlshortener/v1/url?key=<MYAPIKEY>
  -H 'Content-Type: application/json'
  -d '{"longUrl": "http://www.google.com/"}'

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "required",
    "message": "Required parameter: shortUrl",
    "locationType": "parameter",
    "location": "shortUrl"
   }
  ],
  "code": 400,
  "message": "Required parameter: shortUrl"
 }
}