A simple token-based implementation of allowing someone to login as another user in Meteor.
meteor add fongandrew:login-as-user
You'll need to call Accounts.impSvc.set(userId) on the server with the
userId of the user you want to login as. This will return a token you can
use to log in. How you get the token from server to client is up to you, but
you'll probably just want to use a Meteor method.
Note that this package does not provide any permission checking that the person requesting a token to login as someone else is actually authorized to do so. You must implement that part yourself -- e.g. check inside the Meteor method before requesting a token.
Once you have a token on the client, call
Accounts.loginWithImpersonate(token, callback). The callback will return
with an error if it failed or nothing upon success.