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<?php
    /**
    * addContentSecurityPolicy
    *
    * Read :    https://www.owasp.org/index.php/List_of_useful_HTTP_headers
    *           https://www.owasp.org/index.php/Content_Security_Policy_Cheat_Sheet
    *           http://www.html5rocks.com/en/tutorials/security/content-security-policy/
    *           https://www.owasp.org/index.php/Content_Security_Policy
    *           http://content-security-policy.com/
    *
    * Google Analytics requires you to allow 'unsafe-eval' for scripts.  Remove this if you 
    * are using something which does not.
    *
    * @author Andy Beak
    * @date 2014-10-22
    * @version 1.0.0
    * @access private
    *
    */
    private function addContentSecurityPolicy()
    {
        header_remove( 'Content-Security-Policy' );

        // I'm explicitly listing them instead of relying on default so that we can think about each one independently
        $csp = array(
                "default-src 'none'",
                "script-src 'self' 'unsafe-inline' https://apis.google.com https://ssl.google-analytics.com 'unsafe-eval'",
                "object-src 'self'",
                "style-src 'self' 'unsafe-inline'",
                "img-src 'self' https://images.cdn.com/",
                "media-src 'none'",
                "frame-src 'none'",
                "font-src 'self'",
                "connect-src 'self'",
                "form-action 'self'",
                "reflected-xss block",
                "report-uri /security/csp_reports"
            );

        $policy = implode( '; ', $csp );

        $headers = array(
                'X-Content-Type-Options' => 'nosniff',   // protect against drive-by download attacks and sites serving user uploaded content that,
                                                        // by clever naming, could be treated by MSIE as executable or dynamic HTML files.
                'X-XSS-Protection' => '1; mode=block',
                'X-Frame-Options' => 'deny',
                'Strict-Transport-Security' => 'max-age=631138519',
                'Content-Security-Policy' => $policy  // when we are ready stop this from being -report-only and enforce the policy
            );

        foreach( $headers as $header => $value )
        {
            header( $header . ' : ' . $value );
        }

    }