Judge the fields of the incoming array parameters

Judge the fields of the incoming array parameters. A, B, and C are required fields, D, E, and F are possible fields, and other fields must not be present.

/**
 * QUESTION: Judge the fields of the incoming array parameter $params
 *
 * 1. A, B, C are required fields
 * 2. D, E, F are possible fields
 * 3. Others are Fields that must not be present
 *
 * @author yearnfar
*/

//Method 1:
$must = array('A','B','C');
$maybe = array( 'D','E','F');

foreach($must as $key) {
 if (!isset($params[$key])) exit("{$key} must!");
}

foreach($params as $key => $value) {
 if (!in_array($key, $must)) && in_array($key, $maybe)) {
 exit("{$key} Illegal! ");
 }
}

//Method 2:
$fields = array('A' => 1,'B' => 1,'C' => 1,
 'D' => 0,'E' => 0,'F' => 0);

foreach ($params as $key => $value) {
 if (!isset($fields[$key] )) {
 exit("{$key} is illegal!");
 } elseif ($fields[$key]>0) {
 $fields[$key] = 0;
 }
}

if (array_sum ($fields)>0) {//or if (max($fields) > 0)
 exit("Missing required fields");
}

//Method 3:
$fields = array();

foreach ($params as $key => $value) {

 switch ($key) {
 case 'A':
 case 'B':
 case 'C':
 $fields[$key] = 0;
 break;
 case 'D':
 case 'E':
 case 'F':
 break;
 default:
 exit("{$key} is illegal!");
 }
}

if ( count($fields)!=3) {
 exit("Missing required fields");
}