Unable to confirm linked login - required parameter (username) was missing

Testing difficulty: semi-hard, requires custom server with public URL and emailing working, OAuth2 SSO configured and ability to check raw SMTP email contents. Test 1 - confirming a new account Set up a server with OAuth2 authentication enabled (e.g. allow auth via Google) Do NOT prevent account creation when authenticating (authpreventaccountcreation) Attempt to register as a new user via OAuth2 TEST: Check the new account confirmation email. It consists of two mimeparts - one text/plain and one text/html. Make sure that the plain text part has the confirmation URL without & and only the html part has the URL encoded. Test 2 - confirming the linked login Set up a server with OAuth2 authentication enabled (e.g. allow auth via Google) Prevent account creation when authenticating (authpreventaccountcreation) Register a new user manually, set her/his email address to the one you want to use for SSO Log in as the new user via normal Moodle password, do NOT link anything yet Log out On the login screen, attempt to log in via OAuth2 SSO TEST: Check the linked login confirmation email. It consists of two mimeparts - one text/plain and one text/html. Make sure that the plain text part has the confirmation URL without & and only the html part has the URL encoded.