Disallow 'plain' PKCE code challenge
Disallow 'plain' PKCE code challenge

It's less secure and we do not really care about clients that cannot
create a SHA256 hash...

ThiefMaster/indico,pferreir/indico,pferreir/indico,ThiefMaster/indico,DirkHoffmann/indico,ThiefMaster/indico,ThiefMaster/indico,indico/indico,pferreir/indico,pferreir/indico,indico/indico,indico/indico,indico/indico,DirkHoffmann/indico,DirkHoffmann/indico,DirkHoffmann/indico