SAML2\SignedElementHelper::setSignatureKey PHP Method

If the key is null, the message will be sent unsigned.

public setSignatureKey ( XMLsecurityKey $signatureKey = null )
$signatureKey	XMLsecurityKey

    public function setSignatureKey(XMLsecurityKey $signatureKey = null)
    {
        $this->signatureKey = $signatureKey;
    }

SignedElementHelper