Support for OAuth for Okta doesn't handle token expiration

[wikkim]

Referring to code introduced in this PR
https://github.com/okta/okta-sdk-nodejs/pull/128/files
https://developer.okta.com/docs/guides/implement-oauth-for-okta/overview/

The access tokens used for OAuth for Okta feature only last an hour. When using the private_key_jwt authentication access tokens instead of the traditional API Token, this SDK does not renew them so API requests from this SDK will just start failing after an hour. Here is a code snippet to reproduce
https://pastebin.com/N0eLisqU

There should be some additional logic to renew tokens ideally before they even expire.

[swiftone]

Thanks for the report @wikkim and the repro case - we'll investigate. It is supposed to mint a new token on failure and retry.

Internal ref: OKTA-291504