PHP OOP - How to handle authorisation?

Question

I'm building a management system for an idea I have. I'm well versed in PHP (at least enough to do everything I need to do) but I'm not that experienced with using OOP. I use it as much as I can but a lot of the best practices I'm not familiar with so when I do things I worry I'm doing them in the wrong order.

For this project I have a class for the thing the user is managing, I need to check whether or not the user has permissions to manage it. I know how to check the permissions, my question is: where should I be doing it?

Should I be doing it outside the class, like so:

if user permissions are valid
initialize class
else return error

or should I be doing

initialize class
class checks permissions 
class returns error if permissions are invalid

I'm unsure which is the correct approach. On the one hand checking within the class seems the best based on what I know of OOP methodology, but then I also have the feeling that letting it get as far as initializing the class when permissions are unknown might be bad.

How should I be doing it? If there's any sort of article that covers this sort of thing a link would be greatly appreciated (I can't find anything through searches but I'm not 100% sure if I'm searching for the right thing as I know little of OOP)

Answer 1

It depends on what is your permissions model, and there is no "one correct way" to do it. It's a matter of approach. The important thing, is that whatever you choose, you use it consistently.

In my latest projects, I came across several different models. One of the most straightforward is a page-based permission, which is good if you do page-based flow, and use objects for support: you define at the top of the page who is supposed to access it and in case you can redirect. This is the simplest one, but can be very useful on specific applications.

If you, on the contrary, use objects to do your main flow, you should secure your object methods (rather than class instantiation). If you have a "save()" method, which can be called by specific users only, first thing when you enter that method, do your permissions check.

I am currently using an MVC pattern, and I have a Controller, which dispatches the actions to its children. Its only public method is execAction($params) and it will call actionAction($params) on itself, but first it will check permissions.

One important thing to remember is: never present actions on the UI that the user is not allowed to do (unless you are trying to force him to buy your "PRO version", that is) ;-)

Answer 2

I have written a pretty solid and robust CMS system. Here's how I do it and I hope you can extrapolate some information on making your own solution.

• I have an index file, which loads an Admin class. Functionality in my CMS is modular (so containing in its own file and class).
• A module is loaded based on a $_GET parameter.
• Because the function to check the $_GET parameter and load the corresponding function is in my Admin class ($admin->pick_method()) and I also have a User object in my Admin class, I can first check the requested module is in the currently logged in user's permissions array.
• If the permissions check returns true, I load the module. If false, I display a friendly "unauthorized access" page.

Hope this helps.