How do you run one daemon for multiple users?
bitcoin-cli attempts to read the credentials from $HOME/.bitcoin. Since user2 will have a different home directory, bitcoin-cli will not able to find the credentials.

You can either symlink .bitcoin from user1's home directory to user2's, or alias bitcoin-cli for user2 to use -datadir=user1home/.bitcoin.

You may need to play around with the read permissions in either case.