Customize the Thunderbird email client

We're looking for a C++ developer who understands the use of digital identity certificates. This project calls for customizing the Thunderbird version 78 email client so that it facilitates the digital signing of outgoing email messages using certificates issued by our certification authority as well as the proper handling of signed incoming messages. Please see the attached brief functional specification There are so many non experienced developers here, I know about it very well. So If you have really good experience in this field, I would like to provide test assignment. Is it possible to you? If yes, please start proposal with "yes I will do that test !"