convert a xml file to a password protected xlsx

I want to convert a xml file to a password protected MS Excel file on the command line.

The conversion from xml to an unprotected xlsx works fine with:

soffice --headless --convert-to xlsx:"Calc MS Excel 2007 XML" source.xml

My question is: How can I make the xlsx to be password protected?

I am on LibreOffice 4.2.6.3, Build ID: 4.2.6.3-4.el7.