How to add a node with zero downtime

[Cogumelos Maravilha]

Hi list,

I'm using C* 3.10;

authenticator: PasswordAuthenticator and authorizer: CassandraAuthorizer

When adding a node and before |nodetool repair system_auth| finished all
my clients die with:

cassandra.cluster.NoHostAvailable: ('Unable to connect to any servers',
{'10.100.100.19': AuthenticationFailed('Failed to authenticate to ...

Thanks in advance.