Server-side sync_sso rejects valid payloads with 422 "Login Error" when the base64 contains a `+` (triggered by `~` in synced fields)

zogstrip · July 24, 2026, 2:04pm

Thanks for the report @sweetbeems It’ll be fixed by

github.com/discourse/discourse

FIX: Preserve "+" in server-side sync_sso payloads (#42024)

main ← fix-sync-sso-plus-double-decode

merged 02:28PM - 24 Jul 26 UTC

ZogStriP

+51 -19

Previously, `sync_sso` rebuilt its query string from the already form-decoded `p…arams[:sso]` and let `DiscourseConnect.parse` decode it a second time, so any literal `+` in the base64 payload became a space and a correctly-signed request was rejected with a generic 422 "Login Error". This change rebuilds the query with `Rack::Utils.build_query` — the exact inverse of the `parse_query` the parser runs — so the payload is decoded exactly once. The second commit applies the same reasoning to `CookedPostProcessor#remove_user_ids`, which rebuilt link query strings by hand and corrupted encoded values (e.g. `%26`) when stripping the `u=` param. Reported at https://meta.discourse.org/t/407426.

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Server-side sync_sso rejects valid payloads with 422 "Login Error" when the base64 contains a `+` (triggered by `~` in synced fields)

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