Limit who can access dashboard

I have created a series of dashboards for my company´s clients, but need who can access the embedded URL.  Ideally it should be a password protection, but other alternatives could also work. 

It seems like there should be an easy solution for this, but cant seem to solve it. I see it is easy to control access to the underlying editable Looker file, but cant manage to do the same for the embeded URL. Any help is appreciated.

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