TheOAuth feature of Salesforce that should be used to restrict the types of resources mobile users can access is scopes. Scopes are parameters that specify the level of access that the mobile app requests from Salesforce when it obtains an OAuth token. Scopescan be used to limit the access to certain resources or actions, such as API calls, full access, web access, or refresh token. By configuring scopes in the connected app settings, Universal Containers can control what the mobile app can do with the OAuthtoken and protect against unauthorized or excessive access.
References: [OAuth Scopes], [Connected Apps], [OAuth Authorization Flows]

OAuth 2.0 is an open standard for authorization that allows a third-party application to obtain limited access to a protected resource on behalf of auser. To authorize a third-party service using OAuth 2.0 with the Salesforce Experience Cloud site, the identity architect should do the following steps:
* Create a connected app for the third-party service in Salesforce. A connected app is an applicationthat integrates with Salesforce using APIs and standard protocols, such as SAML, OAuth, and OpenID Connect. To create a connected app, you need to provide the basic information, such as the app name, logo URL, contact email, and API name. You also need toenable OAuth and configure the OAuth settings, such as the callback URL, the scopes, and the policies.
* Authorize the third-party service by sending authorization requests to the community-url/services
/oauth2/authorize/expid_value. This is a special endpoint that allows you to specify an experience ID (expid) as a query parameter in the authorization request. The experience ID is a unique identifier for each experience (community or site) in Salesforce. By using this endpoint, you can dynamically render thelogin page images based on the user's brand preference selected in the third-party service before authorization.
References:
OAuth 2.0
OAuth 2.0 Web Server Authentication Flow
Connected Apps
Create a Connected App
Experience ID
Authorize Apps with OAuth

The best option for UC to create the identities of its e-commerce users with the customer community is to use SAML JIT in the customer community to create users when a user tries to login to the community from the e- commerce site. SAML JIT (Just-in-Time) is a feature that allows Salesforce to create or update user accounts based on the information provided in a SAML assertion from an identity provider (IdP). This feature enables UC to avoid duplicating user registration on both applications and provide a seamless single sign-on (SSO) experience for its customers. The other options are not optimal for this scenario. Using the e-commerce REST API to create users when a user self-registers on the customer communitywould require the user to register twice, once on the e-commerce site and once on the customer community, which would degrade the customer experience. Using a nightly batch ETL job to sync users between the customer community and the e- commerce platformwould introduce a delay in user creation and synchronization, which could cause errors or inconsistencies. Using the standard Salesforce API to create users in the community when a user is created in the e-commerce platform would require UC to write custom code and maintain API integration, which could increase complexity and cost. References: [Just-in-Time Provisioning for SAML], [Single Sign-On], [SAML SSO Flows]

B is correct because a third-party product can act as an Identity Provider (IdP) for both Salesforce and Google Apps and manage the user provisioning from a single place12. This reduces the administrative burden and provides a consistent user experience.
D is correct because Salesforce can act as an IdP and Google Apps can act as a Service Provider (SP) and they can use SAML or OpenID Connect for Single Sign-on (SSO)34. Salesforce also supports User Provisioning for Connected Apps, which allows the creation, update, and deactivation of users in Google Apps based on changes in Salesforce.
A is incorrect because building a custom app on Heroku as an IdP is not an optimal way to provision users and allow SSO. It would require more development and maintenanceeffort than using a third-party product or Salesforce as an IdP.
C is incorrect because Identity Connect is a tool that synchronizes users between Active Directory and Salesforce. It does not support Google Apps as a target system for user provisioning orSSO.
References:
1: Architect Journey: Identity and Access Management Trailmix - Trailhead
2: Free Salesforce Identity-and-Access-Management-Architect Questions ...
3: [SingleSign-On Implementation Guide Developer Documentation]
4: [Social Single Sign-On with OpenID Connect Salesforce Developer YouTube]
5: [Authorize Apps with OAuth Trailblazer Community Documentation]
6: Identity Connect Implementation Guide Developer Documentation

Building an integration that performs a remote call-in to theSalesforce SOAP or REST API is the best way to provision Salesforce users as soon as they are approved in the helpdesk application. The API allows creating and updating user records with the approved profiles and permission sets. The other options are either not suitable or not sufficient for this use case. References: User SOAP API Developer Guide, User REST API Developer Guide