I don't think there is a specific event for logins. The closest I got was to use the User Updated event. In the returned object is a property for lastLoginDate. The drawback is that you get this event fired for every update to a user account.
Thanks Jason, I appreciate the feedback. I'm working through a few options to keep our User records (Title & Manager (aka Reports To) synchronized with our HR system (UKG (aka UltiPro) via SSO and Mapping User Attributes. The User Updated event is somthing that may be in the mix.