Advice on template files/sharing externally.

Hello, 

As the title says suggests, I am looking for some advice/documentation/articles on PowerBI Template files and sharing these files externally. 
I have a dashboard which is currently shared internally, but I would like to share this with external clients(All viewers would have PowerBI pro license). I was thinking that a good way to go about this would be to Publish a PowerBI template file, and share this with internal staff/external clients. 
However, security is a concern and I don't want just anybody who happens to obtain the link to be able to open the report/view the data. 

Any advice, documentation or articles would be greatly appreciated as I am new to sharing files externally. 

Thanks in advance, 
Ross