WARNING: The following packages cannot be authenticated!

Solution1:
add suffix--allow-unauthenticated like this：

sudo apt-get install -y mongodb-org --allow-unauthenticated

Solution2:
Connect directly to net (ie avoid the corporate proxy)
Switch off proxy config in Settings and /etc/apt/apt.conf

1. sudo apt-key update
2. sudo apt-get update
3. sudo apt-get install ‘something’