Here is the code I'm using:
$arquivo = "destino.json";
$info = file_get_contents($arquivo);
$lendo = json_decode($info);
foreach($lendo->rotas as $campo){
echo "<b>Origem:</b> ".$campo->origem;
$origin = $campo->origem;
echo "<br /><b>Destino:</b> ".$campo->destino;
$destination = $campo->destino;
}
$key = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
//echo "<br><a href='".$url."' >Calcular Rota</a>";
$url = "https://maps.googleapis.com/maps/api/directions/json?origin=$origin&destination=$destination&sensor=false&key=$key";
echo "<br><a href='".$url."'>URL</a>";
// create curl resource
$ch = curl_init();
// set url
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);
curl_close($ch);
$arr = json_decode($output, TRUE);
echo "<br><br><br>";
echo "";
print_r($arr);