Are there specific cache tags which get reset on user login? Scenario

I'd like to invalidate a set of caches based on user id upon user login. I'd like to avoid creating new tags, and limit new code as much as possible. Presumably the way to do this is with cache tags.

The specific use case is to cache a user-specific web service response, per user, for the duration of a user session.

Are there any existing cache tags (or something to similar effect) which are invalidated upon successful user login, so that I don't have to implement hook_user_login() to manually invalidate the cache?
No, there aren't any cache tags invalidated upon login. And even if there were, they wouldn't be tied to your cache. Instead, you should act on hook_user_login(), and expire the cache yourself.

Cache invalidation isn't really something you would piggy back onto something non-relevant. Rather, you set up elements with cache tags/contexts etc, and then if necessary you add your own cache invalidation on relevant events.