Combining OpenId and OfflineAccess scope

[mcl-sz]

When the client scope is set to "openid offline_access", the returned scope only has the "offline_access" scope. The "openid" scope and the "id_token" are missing. By combining the OpenId and OfflineAccess as return scope, the refresh_token and id_token are returned.

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes

Description

This change checks if the OpenId and/or OfflineAccess scope is set and combines them.
To test I've used the Client app of this repro from Jeroen Breuer: https://github.com/jbreuer/UmbracoDeliveryApiAuthDemo

Change https://github.com/jbreuer/UmbracoDeliveryApiAuthDemo/blob/a799b307302f7189d7ddd69b9554ae2b24612eb4/src/Client/src/App.js#L22 to const scope = 'openid offline_access';

Copy the "OpenIdConnect" section in the appsettings.json to your own installation.

The token result looks like this:

Note that the id_token is missing and the scope is set to "offline_access" only.

After applying this PR, te result looks like this:

[github-actions]

Hi there @mcl-sz, thank you for this contribution! 👍

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[georgebid]

Hey @mcl-sz, thanks a lot for your PR. Someone on the Core Collaborators team will review this soon 😄