fix invalid session start

[HolgerHees]

This will fix errors like A session had already been started

The reason was that there was a already started session and regenerateId() was assigning a new session id to it. So there is no need to call start_session() again.

This will fix #20490

[korelstar]

This fixes the issue for me. Please backport!

[kesselb]

Thank you for sending a patch 👍

Today I run into the change accidentally that is causing that issue: https://github.com/nextcloud/server/pull/17075/files#diff-c68da9343553e4a58b89b1e38a975a70

It seems this issue is present for quite a while but in older versions a new session is started like $this->invoke('session_start', [], true); and true as third parameter silences every error ;)

As the session is only unset and not destroyed it seems reasonable to me that startSession throws an error and I wonder if that is intended. How do we send the new session id to the user after regenerate?

[HolgerHees]

@kesselb can you append your comment to my pull request. just that the other devs are aware of your concerns.

my guess is that regenerate_session id is send the session id to the user, because it is a php core function which will handle this automatically.

[kesselb]

@HolgerHees usually @rullzer read's the comments on a pull request ;)

[MorrisJobke]

This was fixed a little bit different in #22243