如何以数组的形式为curl_setopt()函数固定http标头

$headers = array(
    'Content-Type: application/json'
);

$ch = curl_init();
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$url = 'http://example.com/api';
$data = array('key1' => 'value1', 'key2' => 'value2');
$headers = array(
    'Content-Type: application/json',
    'Authorization: Bearer token'
);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($data));
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$response = curl_exec($ch);
curl_close($ch);

echo $response;