[Plug In] Auto Assign Contributor Passwords

So I’ve been working on my blog – https://www.haharuined.com – and I really just need one simple question to be answered. It seems like this can be answered pretty easily, however, I have not managed to get my answer. The only thing I’ve found out is that I need a plug in, I believe. All I want to be able to do is automatically assign passwords the to contributors who sign up for my blog. PLEASE HELP!