I am developing a module for Drupal 7 which calls a remote API. I am using drupal_http_build_query(), drupal_http_request(), and drupal_json_decode().

My code is as follows

$username = $form_state['input']['name'];
$password = $form_state['input']['pass'];

$authurl = variable_get('sgauth_base_url_authenticate', '');
$headers = array('Content-Type' => 'application/json');
$data = array('email' => $username, 'password' => $password);
$query = drupal_http_build_query($data);
$options = array('headers' => $headers, 'method' => 'POST', 'data' => $query);
$result = drupal_http_request($authurl, $options);

dpm($result);

$authurl is returning the correct url for the API.

When I look at the returned object I see the following

The request is (Note host, username and password have been hidden)

POST /SingPostApi/MobileAuthenticate HTTP/1.0 
Content-Type: application/json 
User-Agent: Drupal (+http://drupal.org/) 
Host: xxxxxxxxxxxx.xxxxxxxxxx.com 
Content-Length: 36

email=xxx%40xx.xxx&password=xxxxxxxx

Which seems OK

$result->code I see a 500 error

$result->data shows Invalid JSON primitive: email.

As far as I can tell my code is OK based on my reading of the Drupal API. I don’t understand why I am getting the wrong data returned.

When I make he POST request from the Firefox HTTP Requester I get a 200 code and the data I expect to see returned

I would appreciate it if someone who can see where I am going wrong can point me in the right direction.