private static byte[] getNullTerminatedAsciiString( final String source )
    {
        final byte[] bytesWithoutNull = source.getBytes(StandardCharsets.US_ASCII);
        final byte[] target = new byte[bytesWithoutNull.length + 1];
        System.arraycopy(bytesWithoutNull, 0, target, 0, bytesWithoutNull.length);
        target[bytesWithoutNull.length] = (byte) 0x00;
        return target;
    }
The signature string as bytes in the default encoding
httpclient5/src/main/java/org/apache/hc/client5/http/impl/auth/NTLMEngineImpl.java