Tapir used human-readable substitutions ('@' -> '-at-', '.' -> '-dot-') when
deriving the Password CR name from an email. Dex's internal passwordID() maps
every non-[a-z0-9-] character to plain '-'. This caused a name mismatch:
Tapir wrote the CR as 'mathias-at-d-ma-dot-be', Dex looked it up as
'mathias-d-ma-be', got not-found, and returned 'Invalid credentials' on every
invite login — while static configmap passwords (a different code path) worked
fine. Diagnosed by adding the email to staticPasswords and confirming login
succeeded, proving the kubernetes CR lookup was the failure point.