Setup a new user for remote SSH from client

add-ssh-user.sh

IP_ADDRESS="0.0.0.0"
EXISTING_REMOTE_USER=root
NEW_REMOTE_USER=user

# Authorize as root
ssh-copy-id $EXISTING_REMOTE_USER@$IP_ADDRESS

# Create user (no interaction needed)
echo "
adduser --disabled-password --gecos '' $NEW_REMOTE_USER
usermod -aG sudo $NEW_REMOTE_USER
echo '$NEW_REMOTE_USER ALL=NOPASSWD: ALL' > /etc/sudoers.d/$NEW_REMOTE_USER
mkdir /home/$NEW_REMOTE_USER/.ssh
cp ~/.ssh/authorized_keys* /home/$NEW_REMOTE_USER/.ssh
chown --recursive $NEW_REMOTE_USER /home/$NEW_REMOTE_USER/.ssh
" | ssh $EXISTING_REMOTE_USER@$IP_ADDRESS

# Start SSH session as new user
ssh $NEW_REMOTE_USER@$IP_ADDRESS