I'm trying to use APIGEE as my authorisation server as an example shown https://build.fhir.org/ig/HL7/smart-app-launch/example-app-launch-public.html#launch-app, how would I set up the .well-known/smart-configuration endpoint? I already have an app and an api for google healthcare FHIR server.
Yes - that is the Health APIX accelerator. It is available through services engagements from partners. In one of my prior replies I gave a link to one of the services providers that does this work (SoftServe).
Would Okta work as an authorization server that can do the same?
Okta will act as an Open ID Connect provider, and will expose a "well known endpoint" for OpenID Connect. This is not the same as a well known endpoint that can be used to support FHIR Smart Launch.
"well known endpoint", is a generic term that describes an HTTP accessible endpoint that returns configuration information - see Wikipedia. Or, IETF RFC 8615 which defines "Well known URI". The information domain can be "anything", and there are many kinds of well-known endpoints. for example,
So, Okta will not help you directly with FHIR Smart Launch.