This job is very straightforward if you are skilled in codeigniter framework.
I have installed codeigniter already on the development server you get access to during development.
And the project has already a working and running Tank Auth authentication library for CodeIgniter.
In the Tank Auth mysql table I have admin and user accounts
If an admin is logged in, all functions become available.
If a user is logged in, the script you are implementing needs to have restrictions.
You need to implement the http://www.mytinytodo.net/ todo list script.
Not just implement it, but first convert it to a the codeigniter MVC style.
After that, if an admin (me) is logged in, I get the full functionality of the todo script and can see all the lists (see subtabs)
If a user is logged in (my client), it needs to redirect to his own list and the user can only add,edit etc in his own list and can't see the other lists (tabs) from other clients.
Also the settings options etc are not accessible by the user.
Easy to implement, but be sure you are skilled enough with codeigniter to convert the non-framework tod0 script from http://www.mytinytodo.net/ to a proper MVC model.