Add optional OAuth2 resource parameters

[fredrikhr]

RFC 8707 Resource Indicators for OAuth 2.0 defines the resource parameter in an OAuth2 token request.

[This RFC defines] request parameters that enable a client to explicitly signal to an authorization server about the identity of the protected resource(s) to which it is requesting access.

Some Token Authorization services require the use of the resource parameter in addition to or instead of the scope and audience parameters for multi-tenant or multi-service scenarios.

An example of this is the Azure Access Control Service which is used to obtain App-Only access tokens for SharePoint Online. The resource parameter controls for which SharePoint online instance the access is granted instead of issuing an access token for all possible SharePoint services.

In httpyac the resource parameter should be optional and behave very similar to the audience parameter.

[AnWeber]

thx