Reauthenticating Users

I wish to know if there is a way to reauthenticate a user?
I have lot of spam users before I installed bot checks on my WP and is there a way ‘non-manual’ way to identify who is a ‘bad user’.
A possible solution for me is to change everyone to sort of ‘hold’ mode [WP equivalent for someone who has registered but not confirmed] [do not know how to do this in db] and resend an email [how?]. IF the user is not confirmed just remove them after ‘x’ days