src/core/Request.php
public function getServerParam(
        string $name,
        int $filter = \FILTER_DEFAULT,
        $options = null
    ) {
        // Can be useful if FastCGI has strange side-effects with unexpected null
        // values when using INPUT_SERVER and INPUT_ENV with this function.
        //return isset($_SERVER[$name]) ? filter_var($_SERVER[$name], $filter, $options)
        //    : null;
        return filter_input(\INPUT_SERVER, $name, $filter, $options);
    }
public function getServerParam(
        string $name,
        int $filter = \FILTER_DEFAULT,
        $options = null
    ) {
        // Can be useful if FastCGI has strange side-effects with unexpected null
        // values when using INPUT_SERVER and INPUT_ENV with this function.
        //return isset($_SERVER[$name]) ? filter_var($_SERVER[$name], $filter, $options)
        //    : null;
        return filter_input(\INPUT_SERVER, $name, $filter, $options);
    }
The method returns the server parameter value by the key. It's wrapper over
the filter_input() function.
@param string $name Name of a variable to get.
@param int $filter
@param mixed $options Associative array of options or bitwise disjunction
of flags. If filter accepts options, flags can be provided in "flags"
field of array.
@return mixed Value of the requested variable on success, false if the filter
fails, or null if the variable is not set.