Possibly bug with readonly sessions

[brendanheywood]

I think the issue is here:

https://github.com/catalyst/moodle-tool_mfa/blob/master/classes/manager.php#L188-L194

It might be that we need to render the page into a var, then logout (which sets headers), then display echo the var

2020/06/10 10:55:34 [error] 236 #236: *10691 FastCGI sent in stderr: "PHP message: Cannot terminate session properly - headers were already sent in file: /var/www/site/admin/tool/mfa/classes/manager.php on line 188 #012PHP message: PHP Warning: session_regenerate_id(): Cannot regenerate session id - headers already sent in /var/www/site/lib/classes/session/manager.php on line 672 #012PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/site/admin/tool/mfa/classes/manager.php:188) in /var/www/site/lib/classes/session/manager.php on line 633#012PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/site/admin/tool/mfa/classes/manager.php:188) in /var/www/site/lib/classes/session/manager.php on line 640#012PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/site/admin/tool/mfa/classes/manager.php:188) in /var/www/site/lib/classes/session/manager.php on line 640#012PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at /var/www/site/admin/tool/mfa/classes/manager.php:188) in /var/www/site/lib/classes/session/manager.php on line 640#012PHP message: PHP Warning: ... repeats a lot