// likely stored in configuration somewhere
$request_config = (object) [
    'https_required' => true,
    'https_forward_allowed' => true
    'http_accept' => [
        'application/json' => true,
        'xml/text' => false
    ],
    // other configurations you may need to validate a request or perhaps
    // determine its routing
];

$response_config = (object) [
    'cors_headers' => [
        'Access-Control-Allow-Origin: *',
        'Access-Control-Allow-Headers: origin, content-type, accept, authorization',
        'Access-Control-Allow-Methods: POST'
    ],
    'content-type' => 'application/json'
    // any other things you may want to configure in response
];

// instantiate response object based on configuration
try {
    // perhaps throw exception if configuration is bad
    $response = new Response($response_config);
} catch (Exception $e) {
    error_log(
        'Unable to build Response object. '
         . 'Exception message: "' . $e-getMessage . '"'
    );
    http_response_code(500);
    exit;
}

// try to build a valid request object
try {
    // instantiate request object
    // this instantiation should throw Exception (with reason) if you
    // get an unexpected request.
    // this request object constructor could check request headers
    // against expected values, try to to marshall (json_decode) the POSTed data
    // etc. and fail out with exception if request falls outside expected.
    $request = new Request($request_config);
} catch (Exception $e) {
    error_log(
        'Unable to build Resquest object. '
         . 'Exception message: "' . $e-getMessage . '"'
    );
    $response->set_error_code(400);
    $response->set_error_message('Bad Request');
    // call method which sends response, but would also be responsible
    // for sending appropriate method (like with internal class class to 
    // (send_headers()) or similar method.
    $response->send();
    exit;
}

// now you have valid Request object you can work with and do things like:
$post_data = json_decode($request->raw_input);

// maybe pass to the posted data to some class or otehr logic which builds
// a data structure for return.
$response->set_data(json_encode($some_data));
$response->send();
exit;

// likely stored in configuration somewhere
$request_config = (object) [
    'https_required' => true,
    'https_forward_allowed' => true
    'http_accept' => [
        'application/json' => true,
        'xml/text' => false
    ],
    // other configurations you may need to validate a request or perhaps
    // determine its routing
];

$response_config = (object) [
    'cors_headers' => [
        'Access-Control-Allow-Origin: *',
        'Access-Control-Allow-Headers: origin, content-type, accept, authorization',
        'Access-Control-Allow-Methods: POST'
    ],
    'content-type' => 'application/json'
    // any other things you may want to configure in response
];

// instantiate response object based on configuration
try {
    // perhaps throw exception if configuration is bad
    $response = new Response($response_config);
} catch (Exception $e) {
    error_log(
        'Unable to build Response object. ' .
        'Exception message: "' . $e-getMessage . '"'
    );
    http_response_code(500);
    exit;
}

// try to build a valid request object
try {
    // instantiate request object
    // this instantiation should throw Exception (with reason) if you
    // get an unexpected request.
    // this request object constructor could check request headers
    // against expected values, try to to marshall (json_decode) the POSTed data
    // etc. and fail out with exception if request falls outside expected.
    $request = new Request($request_config);
} catch (Exception $e) {
    error_log(
        'Unable to build Request object. ' .
        'Exception message: "' . $e-getMessage . '"'
    );
    $response->set_error_code(400);
    $response->set_error_message('Bad Request');
    // call method which sends response, but would also be responsible
    // for sending appropriate method (like with internal class class to 
    // (send_headers()) or similar method.
    $response->send();
    exit;
}

// now you have valid Request object you can work with and do things like:
$post_data = $request->get_post_data();

// maybe pass to the posted data to some class or otehr logic which builds
// a data structure for return.
$response->set_data(json_encode($some_data));
$response->send();
exit;