Introducing Sign in with Slack

Interesting track for Slack to take. Curious about a couple of things in case anyone from Slack is listening:

1. Why not use OpenID Connect (http://openid.net/connect/) on top of OAuth?

2. How does this compare to Okta, Ping, etc.? Seems like this may be a solved problem in the enterprise space and I'm curious what Slack brings to the table that couldn't be done with existing solutions.