Ability to login to multiuser using javascript

**Is your feature request related to a problem? Please describe.**
currently there's no elegant way to login to multiuser plugin using only javascript

**Describe the solution you'd like**
i want a easy and concise way to login to X masterseed autonomously with 0 user input and only using javascript
ideally also having a new site perm like "multiuser manage"

**Describe alternatives you've considered**
the farthest possible is to prompt user for the masterseed input
the only way right now is to also get a userscript to act on your behalf filling in the masterseed form
which can get messy trying to communicate out of iframe and back into iframes