Hello again. I'm still developing my project wich I've uploaded to GitHub (in case you wanted to check it out if you were interested. And don't worry, I'll credit you when it's done :P). This time I needed to pass variables to be retrieved after the user logs in, and the framework currently didn't have support for that. So, I've added it, and I've uploaded it to my fork, in case you wanted to consider merging it. Here's how it works.

The steamlogin() function works as usual. The only change is that you now have to put echo before calling it: the function itself won't echo the button anymore, you have to manually do it. Why? Felxibility. Sometimes you don't need the button to be echoed immediatly, but stored it in a variable to maybe pass it as a parameter to a method. For example, in my script I pass the button as a parameter to the method Modal::__construct(). The class will create a Bootstrap Modal later, and include the button on it. If steamlogin() did echo instead of return I'd need to modify my entire class; this way is much more convenient.

So, any app that ran

steamlogin();

should now run

echo steamlogin();

And now, the most important change. If you want to pass variables to be returned after the login, you'd do the following:

echo steamlogin("foo=1&bar=2");

Notice that you don't have to put any ?s and &s at the beginning.
In that case, you can use $_GET['foo'] and $_GET['bar'] on your login page (set on the settings), and they will be set to 1 and 2, respectively. Assuming that your return URL is http://website.com/index.php, the user will be redirected to http://website.com/index.php?foo=1&bar=2 after loging in successfully on Steam.

One last change: the line session_start() at line 37 on the old file was removed because it's already called at the beginning, so I believe that there's no point on calling it again (In fact, it gives you a warning)

Thanks for your time, and have a nice day!