SSO fails for some existing users

Hello,

after upgrading to 2026.5.0 and the matching SSO tag, I am facing issues for (some) existing SSO users.

The error is coming from https://github.com/cryptpad/sso/blob/7c44ebba5ba83674cc2d47b8176f4b88f4fc9fd7/challenge.js#L236-L239
On the client I see 500 for the respective api call in the console, no details.

I worked around the issue by commenting out the block of code in question, it seems to be new in this release.

Additionally, every time a user tries to log in (clicks the login button on the front page), the following error is shown in the browser console:
/api/auth/ 500 (Internal Server Error)
The response content is
{"error":"Execution error","errorCode":"E_REQ_WRITE"}

The UI shows a red "Error" banner. Refreshing the page results in the same error, the user has to refresh the page without cache and is then correctly redirected to the SSO login page.

Not sure if the two issues are related.