actually send content-type header

pam/auth_client.c

@@ -183,7 +183,7 @@ int auth_client_authenticate(auth_client_t ac,
   curl_easy_setopt(ac->c, CURLOPT_POSTFIELDSIZE, form.size);
 
   // Set request headers.
-  curl_slist_append(headers, "Content-Type: application/x-form-www-urlencoded");
+  headers = curl_slist_append(headers, "Content-Type: application/x-www-form-urlencoded");
   curl_easy_setopt(ac->c, CURLOPT_HTTPHEADER, headers);
 
   // Iterate over the known servers. We create a new response buffer