PayPal\Auth\Oauth\OAuthSignatureMethodRsaSha1::build_signature PHP Method

    public function build_signature($request, $consumer, $token)
    {
        $base_string = $request->get_signature_base_string();
        $request->base_string = $base_string;
        // Fetch the private key cert based on the request
        $cert = $this->fetch_private_cert($request);
        // Pull the private key ID from the certificate
        $privatekeyid = openssl_get_privatekey($cert);
        // Sign using the key
        $ok = openssl_sign($base_string, $signature, $privatekeyid);
        // Release the key resource
        openssl_free_key($privatekeyid);
        return base64_encode($signature);
    }