src/XdrModel/SignerKey.php
public static function fromHashX($x)
    {
        $signerKey = new SignerKey(static::TYPE_HASH_X);
        $signerKey->key = hash('sha256', $x, true);

        return $signerKey;
    }
public static function fromHashX($x)
    {
        $signerKey = new SignerKey(static::TYPE_HASH_X);
        $signerKey->key = hash('sha256', $x, true);

        return $signerKey;
    }
Adds the value of $x as a signer on the account

@param $x
@return SignerKey