Login another user with only username when I am the administrator

I am developing a chat in our app which connects to RocketChat through their Rest api and websocket. I think that is an awesome project by the way!!
My question is regarding login the user. Since our own server creates and login user into RocketChat through REST api, it does make sense to allow to login a third user only with its email, since the server authenticates as full administrator?
This question regards with the fact that we are creating users with a random password, because we don’t manage the plain passwords from our customers. So we ‘simulate’ the creation of the user just to get the auth token. But when we lost it, the only way to relogin the user is with username and password. Maybe I am wrong, but I think is the only way.
What do you think, is that possible?