SpotifyWebAPI\Session::refreshAccessToken PHP Method

    public function refreshAccessToken($refreshToken)
    {
        $payload = base64_encode($this->getClientId() . ':' . $this->getClientSecret());
        $parameters = ['grant_type' => 'refresh_token', 'refresh_token' => $refreshToken];
        $headers = ['Authorization' => 'Basic ' . $payload];
        $response = $this->request->account('POST', '/api/token', $parameters, $headers);
        $response = $response['body'];
        if (isset($response->access_token)) {
            $this->accessToken = $response->access_token;
            $this->expirationTime = time() + $response->expires_in;
            return true;
        }
        return false;
    }