After upgrading to Magento Community 2.2.6 the setup wizard required me to enter my access keys again. Every time I try to add my public and private keys from my Magento Marketplace account the server returns the following error:
Invalid response line returned from server: HTTP/2 200
The actual response from the /setup/index.php/marketplace/save-auth-json call is {"success":false,"message":"Invalid response line returned from server: HTTP/2 200 \r\n"}
Magento 2.2.6 Apache/2.4.37 PHP 7.1