Ah, I see now. You want to share a login token from inside Unity to a web view hosted inside the Unity application, which also visits a meteor website.
Yes. You can simply call the Javascript Meteor.loginWithToken(token, (err, res) => { }) with that token, and you’ll be logged in.
If you’re hosting a web view inside your Unity application anyway, I’d recommend using its internal Meteor connection anyway, by exposing a basic API. It’s relatively easy to proxy objects in Javascript. However, it’s a lot of IT, and if you have something working already, go for it!