ssh/tailssh: use a local error instead of gossh.ErrDenied #10743
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ErrDenied was added in [our fork of x/crypto/ssh](golang/crypto@acc6f8f) to short-circuit auth attempts once one fails. In the case of our callbacks, this error is returned when SSH policy check determines that a connection should not be allowed. Both `NoClientAuthCallback` and `PublicKeyHandler` check the policy and will fail anyway. The `fakePasswordHandler` returns true only if `NoClientAuthCallback` succeeds the policy check, so it checks it indirectly too. The difference here is that a client might attempt all 2-3 auth methods instead of just `none` but will fail to authenticate regardless. Updates #8593 Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
rhealitycheck
approved these changes
Jan 5, 2024
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ErrDenied was added in our fork of
x/crypto/ssh to short-circuit auth attempts once one fails.
In the case of our callbacks, this error is returned when SSH policy check determines that a connection should not be allowed. Both
NoClientAuthCallbackandPublicKeyHandlercheck the policy and will fail anyway. ThefakePasswordHandlerreturns true only ifNoClientAuthCallbacksucceeds the policy check, so it checks it indirectly too.The difference here is that a client might attempt all 2-3 auth methods instead of just
nonebut will fail to authenticate regardless.Updates #8593