Ubuntu – Is first Ubuntu user root

Haven't tried it but this should create a new user and add them to the sudo group, which if your /etc/sudoers is as default, should mean they're allowed to use sudo with their password (just like the standard first user):

sudo adduser --group sudo newusername

If you've already created the user, you can just run:

sudo adduser existing_user sudo

man adduser will show you some of the other billion permutations and combinations of arguments this tool has.

Note: If you use Ubuntu 11.10 or older, you should use the admin group instead of sudo.

Do not put the script in the user's home directory. Instead, put it in a fixed location. If the script needs some user-dependent arguments, make the script read that from a file — but you don't even need that since you're copying the script from /etc/skel anyway.

If you allow a user to run a script in their home directory with elevated privileges, then they can replace the script by another script. So your proposed rule would be equivalent from a security point of view to

ALL ALL=(ALL) NOPASSWD: /etc/skel/createSambaShare.php
MANY ALL=(ALL) NOPASSWD: ALL

where MANY is any user whose home directory is under /home/DOMAIN. (Ok, unless a user's home directory is owned by root, not writable to the user, and the script is not writable by or owned by the user either. But that would be pretty unusual.)

Also, I recommend not using ALL in a User specification. Restrict the rule to a group.

%sambasharers ALL=(ALL) NOPASSWD: /usr/local/bin/createSambaShare.php