Improve OIDC code flow concept document

[sberyozkin]

Fixes #37422

Keeping in a draft state for now, @fedinskiy, please clarify how did you reproduce a too large session cookie issue with UserInfo

[github-actions]

🙈 The PR is closed and the preview is expired.

[rsvoboda]

Hi Sergey. Fedor is on Christmas PTO already, he will be back in January.

[sberyozkin]

Hi Rostislav, sure, sounds good, FYI I'll be totally offline the week starting 8th Jan, but UserInfo related doc updates can be handled separately if we won't address them earlier

[sberyozkin]

@fedinskiy FYI, the large session cookie issue is addressed in #37891, which has already been approved by @gastaldi, so it is ready to go pending some possible comments from Pedro. I plan to merge in the evening of 3rd Jan or 4th Jan morning at the latest, so then it would be possible to verify it fixed the issue in your reproducer as well

CC @rsvoboda

[fedinskiy]

@sberyozkin do you still need clarification regarding large session cookie?

[sberyozkin]

@fedinskiy I'm certain #37891 will resolve it, so if you are OK with it, your comment about it can be considered resolved and then once #37891 is merged, you can double check it if you will have time, does it sound reasonable ?

[rsvoboda]

Approving, @fedinskiy told me he was OK with the changes.

[sberyozkin]

Thanks @fedinskiy @rsvoboda