Can't connect as different user while accessing network share with in domain network in Mac
I am having the same issue. I am logged in with userA. I can see all of the shares. I want to access a specific share that userA does not have access to that userB does. I disconnect from server, but 'connect as' does not do anything when I click it

I found a workaround: 


Go to Finder
Click Go, then Connect to Server
Create a path of smb://userB@myserver


Source: https://discussions.apple.com/thread/7988659?answerId=31890794022#31890794022