What's going on with this program?

A program in Laravel

IlluminateFoundationHttpMiddlewareVerifyCsrfToken

    /**
     * Determine if the session and input CSRF tokens match.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return bool
     */
    protected function tokensMatch($request)
    {
        $sessionToken = $request->session()->token();

        $token = $request->input('_token') ?: $request->header('X-CSRF-TOKEN');

        if (! $token && $header = $request->header('X-XSRF-TOKEN')) {
            $token = $this->encrypter->decrypt($header);
        }

        if (! is_string($sessionToken) || ! is_string($token)) {
            return false;
        }

        return hash_equals((string) $request->session()->token(), (string) $token);
    }

I can’t understand it at all (I mean the writing, not the function).

The above introduces what is going on in this program? , including relevant content, I hope it will be helpful to friends who are interested in PHP tutorials.