Token Mismatch issue in IFrame in Internet Explorer. Laravel 5.2

What's the problem ?

I am facing Token Mismatch issue when accessing the site in IFrame in Internet Explorer.

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What I tried so far ?

I search for the resolution and found this link

Below is the code that I found in the above link

App::after(function ($request,$response){
    if($request->is('external/*')){
        // IE iframe cookie fix
        $response->header('P3P', 
                  'CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT"');
    }
});

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What's the question ?

Where should I write the above code in Laravel 5.2 ?

via Chebli Mohamed