I wouldn't say they're the same thing except from a brand name perspective. Okta is barely app-focused; much more enterprise SSO. Auth0 is extremely app-focused, although they can do some enterprise SSO as well.

Okta bought Stormpath (and killed it) and now Auth0 because of this difference, and because there's a finite total addressable market for employees, but an almost infinite total addressable market for app users.