ParagonIE\CSPBuilder\CSPBuilder::compileSubgroup PHP Method

    protected function compileSubgroup(string $directive, $policies = null) : string
    {
        if ($policies === '*') {
            // Don't even waste the overhead adding this to the header
            return '';
        } elseif (empty($policies)) {
            if ($directive === 'plugin-types') {
                return '';
            }
            return $directive . " 'none'; ";
        }
        $ret = $directive . ' ';
        if ($directive === 'plugin-types') {
            // Expects MIME types, not URLs
            return $ret . \implode(' ', $policies['allow']) . '; ';
        }
        if (!empty($policies['self'])) {
            $ret .= "'self' ";
        }
        if (!empty($policies['allow'])) {
            foreach ($policies['allow'] as $url) {
                $url = \filter_var($url, FILTER_SANITIZE_URL);
                if ($url !== false) {
                    if ($this->supportOldBrowsers) {
                        if (\strpos($url, '://') === false) {
                            if ($this->isHTTPSConnection() || !empty($this->policies['upgrade-insecure-requests'])) {
                                // We only want HTTPS connections here.
                                $ret .= 'https://' . $url . ' ';
                            } else {
                                $ret .= 'https://' . $url . ' http://' . $url . ' ';
                            }
                        }
                    }
                    if ($this->isHTTPSConnection() || !empty($this->policies['upgrade-insecure-requests'])) {
                        $ret .= \str_replace('http://', 'https://', $url) . ' ';
                    } else {
                        $ret .= $url . ' ';
                    }
                }
            }
        }
        if (!empty($policies['hashes'])) {
            foreach ($policies['hashes'] as $hash) {
                foreach ($hash as $algo => $hashval) {
                    $ret .= \implode('', ["'", \preg_replace('/[^A-Za-z0-9]/', '', $algo), '-', \preg_replace('/[^A-Za-z0-9\\+\\/=]/', '', $hashval), "' "]);
                }
            }
        }
        if (!empty($policies['nonces'])) {
            foreach ($policies['nonces'] as $nonce) {
                $ret .= \implode('', ["'nonce-", \preg_replace('/[^A-Za-z0-9\\+\\/=]/', '', $nonce), "' "]);
            }
        }
        if (!empty($policies['types'])) {
            foreach ($policies['types'] as $type) {
                $ret .= $type . ' ';
            }
        }
        if (!empty($policies['unsafe-inline'])) {
            $ret .= "'unsafe-inline' ";
        }
        if (!empty($policies['unsafe-eval'])) {
            $ret .= "'unsafe-eval' ";
        }
        if (!empty($policies['data'])) {
            $ret .= "data: ";
        }
        return \rtrim($ret, ' ') . '; ';
    }