Could be as simple as "number of companies that need auth x number of employees of that company x average cost per seat for Okta/Auth0".

Now, figuring out some of those numbers is harder. Okta simplest pricing is $2 per person per month, but to really us it you are looking at paying more like $15 a month. So, per user it's $180 a year. 30 billion / 180 = 166 million users. If average company size is 500, that's 330k companies, which is a lot.

Anyway, those are just very quick back of the napkin numbers. I would guess they've done a little more work to come up with the number.

(pls forgive any math errors/rounding!)