What is the lifespan of tokens ffrom ringcentral oauth server

Let's answer one by one.

Is there any documented life span for both the tokens generated?

What is the longevity of access_token and refresh_token?

Access token lifetime is 3600s = 1 hour

Refresh token lifetime is 7 days(1 week)

you can refer: https://forums.developers.ringcentral.com/articles/1426/generating-access-token-and-refresh-token-and-effi.html

Can this be configurable?

I don't think so

Is there some way I configure the oauth call not to generate refresh_token?

Yes, you can. Just use refresh_token_ttl=0 in the OAuth request along with your other parameters like grant_type, extension etc.

You will not display refresh_token as it will expire before it display in response and you can skip that in your API response.