I'd like to see SSPR able to complete OAuth without the requirement of OSP or NAM to allow it to become a more standalone product.
At this stage I can configure SSPR to use a 3rd party IdP (Okta) to receive the OAuth token now that SSPR 4.5.0.4 has ''Skip Auth header in OAuth Code Resolve Request' as a selection in the configuration editor.
The next step is to have SSPR complete the query to the Identity Server (e.g. eDir) to return attribute data on the user as is normally configured under "OAuth Profile Service URL" to complete the OAuth flow.
Perhaps by using the proxy user account you can query for this?