There are libraries for doing this, but it's ultimately up to each site/service to implement. I maintain an add-on for Django that does this, for example, but

There are libraries for doing this, but it's ultimately up to each site/service to implement. I maintain an add-on for Django that does this, for example, but I can't force people to go and use it, though I also maintain one of the more popular user-registration apps and I probably will find a way to enable it by default in there.