To enable Azure AD authentication for App1, use Azure AD application
To implement access requests for App1, use an access package in identity governance

To enable Azure AD authentication for App1 and provide access security, the recommended solution is to use an Azure AD application. You should create an Azure AD application, configure the necessary permissions, and assign users and groups to the application.

An access package in identity governance should be used to implement access requests for App1. Identity Governance provides access packages that allow users to request access to specific applications, groups, or roles. The request is routed to the appropriate approver, who can either approve or reject the request. Access packages can be created, managed, and assigned in the Azure portal, and can be customized to include specific access policies and permissions. This provides a streamlined and secure way to manage access to App1, ensuring that only authorized users can access sensitive data or resources....

I would go for:
a) Azure AD application (https://docs.microsoft.com/en-us/azure/active-directory/manage-apps/what-is-application-management)
b) An access package in identity governance (https://docs.microsoft.com/en-us/azure/active-directory/governance/entitlement-management-access-package-create)