'Calling L{checkers.SSHPublicKeyChecker.requestAvatarId} with
credentials that are incorrectly signed fails with
L{UnauthorizedLogin}.'

def test_credentialsInvalidSignature(self):

    self.credentials.signature = keys.Key.fromString(keydata.privateDSA_openssh).sign('foo')
    self.failureResultOf(self.checker.requestAvatarId(self.credentials), UnauthorizedLogin)
