Sharepoint - Calling user profile service from SharePoint Designer 2013 workflow yields "unauthorized"

The workflow app, by default, doesn't have access to the UserProfile for REST calls

Try following these steps to grant the workflow more rights:

Go to your site collection settings and click on App permissions (/_layouts/15/appprincipals.aspx?Scope=Web)
Make note of the App ID for your Workflow - it will be the GUID between i:0i.t|ms.sp.ext| and the @ sign
Go to your site collection's appinv.aspx page (/_layouts/15/appinv.aspx)
At the appinv.aspx page, fill in the Application ID and click the search button next to the ID box
Fill out the permission request box with the XML detailing the permissions you would like to grant (examples in the reference page)
- In your case I would try:
```
  <AppPermissionRequests>
    <AppPermissionRequest Scope="http://sharepoint/social/tenant" Right="Read" />
  </AppPermissionRequests></li>
```

Reference: http://msdn.microsoft.com/en-us/library/office/fp142383(v=office.15).aspx

You might also try adding a AppOnlyStep and enabling the web feature "Workflow Can Use App Permissions"

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