Further note: we've now learned that this issue also **prevents users from posting** on discussions.apple.com (though they can edit their earlier posts). See bug 1999667 for notes/details on that. (Presumably discussions.apple.com uses the same HTTP-header-parsing/validation logic in both of these cases -- for username-availability checking [this bug] and also for one of the http-requests involved in making posts [bug 1999667]. So both workflows are broken if this `Idempotency-Key: "[something]"` header is present -- likely due to the server choking on the double-quoted string, per comment 10.)
Bug 1940594 Comment 21 Edit History
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Further note: we've now learned that this issue also **prevents users from posting** on discussions.apple.com (though they can edit their earlier posts). See bug 1999667 (particularly bug 1999667 comment 8) for notes/details on that. (Presumably discussions.apple.com uses the same HTTP-header-parsing/validation logic in both of these cases -- for username-availability checking [this bug] and also for one of the http-requests involved in making posts [bug 1999667]. So both workflows are broken if this `Idempotency-Key: "[something]"` header is present -- likely due to the server choking on the double-quoted string, per comment 10.)