Add private key passphrase option to decryptSoapDoc

[cmmcneill]

Added an option to decryptSoapDoc named 'passphrase' so that an encrypted private key can be used to decrypt a document without manually decrypting the key beforehand.

Example:

$wsse = new WSSESoap($doc);
$options = [
    'keys' => [
        'private' => [
            'key' => $encryptedPrivateKey,
            'passphrase' => $privateKeyPass
        ]
    ]
];
$wsse->decryptSoapDoc($doc, $options);

[robrichards]

Thanks!