#844: a success cleared the whole per-client count, so a client holding a valid
key could make four guesses at another key id, sign in with its own, and repeat
forever. Failures are now charged to the (client, credential identity) pair --
IOpcUaUserAuthenticator.DescribeCredential, key:<keyId> for API keys -- and to
the client as a whole. A success clears only its own identity's count; the
per-identity threshold locks that identity; a new per-client cap
(OpcUa:CredentialLockout:MaxFailedAttemptsPerClient, default 2 x
MaxFailedAttempts) that a success never resets bounds spraying across key ids
and locks every credential. Slots are bounded on both counts; a waiter whose
identity has room is not held behind one whose identity has none.
#845: (1) store timeouts, miss-budget refusals, store/authenticator exceptions,
an unset pepper and cancellation are reported Transient
(OpcUaUserAuthResult.Unavailable) and released uncounted, so a ConfigDb stall
can no longer lock every keyed client out; the client still sees the same
opaque denial. (2) a full 4096-entry table defers its next prune until the
earliest entry could age out instead of rescanning under the lock per failure.
(3) ApplicationUri deliberately NOT added to the key: on a None channel it is a
free string, so it would let an attacker reset the count per guess --
documented. (4) wire tests: distinct client certificates on a Sign endpoint are
locked out separately; the ApplicationConfigPath branch keeps the SDK lockout
off (falsified by removing the loaded-branch disable).
Joseph Doherty
ffba75bb93