Oauth endpoints - rate limted?


The documentation at https://dev.twitter.com/oauth/reference/get/oauth/authorize indicates that the call is rate limited. But what is the rate?

I understand the rate limits for the various API calls “after” authentication is handled, but I don’t see any information on the specific limit during an authentication.

Basically, how many authentications per minute, hour, etc can this endpoint handle. What if I get a spike of user registrations where we are using Twitter to authenticate?