Integrating Microsoft Entra ID with a Svelte SPA and ASP.NET Core API: Managing API Scopes and Dynamic User Claims

Below is an explanation addressing your questions:

1. What Do These API Scopes Do?

• Definition and Purpose
  When you define scopes (such as AdminTool.Read) in the "Expose an API" configuration, you are declaring the permissions that a client (for example, your Svelte SPA) can request when calling the Web API. These scopes serve as a contract that both the API and the client agree upon to authorize access.

• Application-Level vs. User-Level
  Although the scopes are checked on every token the client presents, they are defined statically and apply to the API as a whole. In other words, they are used to control which APIs the client can access, not to inherently enforce fine-grained, per‑user authorization decisions. In your example, if the token does not contain the custom scope (AdminTool.Read), the API rejects the request.
  However, these scopes do not automatically translate into dynamic, per‑user permissions.

2. Implementing User‑Specific Permissions Dynamically

• Why You Can’t (Easily) Use API Scopes for Dynamic, Per‑User Rights
  The scopes that you define in Entra ID (Azure AD) under "Expose an API" are static. Their purpose is to gate the API at an application/delegated level rather than modify individual user privileges on a granular basis.

• Recommended Approach: Use Roles or Claims
  To support dynamic, per‑user permissions (for example, adding permissions like Dashboard.Read on a per‑user basis), you should consider:

  • App Roles:
    Define application roles in Entra ID that can be assigned to users or groups. Roles represent permission levels on a per‑user basis. When a user signs in, the assigned roles can be placed as claims in the token, and your API can enforce authorization based on those role claims.

  • Custom Claims:
    Use attributes or custom claims to capture user-specific permissions. For example, you can add claims via Microsoft Graph or a custom claims transformation in ASP.NET Core. This can allow you to dynamically adjust the privileges (like Dashboard.Read) without needing to update the statically defined scopes.

  • Graph API for User Assignment:
    The Microsoft Graph API lets you modify group or role assignments for users. Instead of trying to create a new scope per user, you assign users to groups or roles that have claim mapping which represents the permissions you want them to have. This is the best practice when defining dynamic, granular permissions.

• Best Practice Summary:

  1. Keep API Scopes Static:
     Use the scopes (e.g. AdminTool.Read) for overall API protection and for ensuring that only properly consented clients can call the API.

  2. Implement Fine-Grained Authorization via Claims:
     – Define a small set of well-known roles or claim types in your directory.
     – Update users’ or groups’ assignments dynamically (via Graph API or other user management methods).
     – In your API, use ASP.NET Core’s policies (or custom claims transformation) to enforce these permissions per user.

  3. Ensure Your API Evaluates the Claims:
     For example, in your ASP.NET Core Web API you might have an authorization policy that checks for a particular claim when a user requests access to a dashboard:

     CSHARPCopied
     services.AddAuthorization(options =>
     {
         options.AddPolicy("Dashboard.ReadPolicy", policy =>
             policy.RequireClaim("permissions", "Dashboard.Read"));
     });

     And then decorate your controller or action method:

     CSHARPCopied
     [Authorize(Policy = "Dashboard.ReadPolicy")]
     public class DashboardController : ControllerBase
     {
         // Your actions here
     }

Final Thoughts

• The custom scope you defined (AdminTool.Read) is meant for access control at the API level.
• To handle dynamic, per‑user permissions, consider using app roles or custom claims that you manage (for example, via the Graph API).
• Then, enforce the user-specific permissions in your API using claim-based authorization policies.

This approach follows best practices for using Entra ID (Azure AD) with Web APIs and ensures that while your API is secured in a coarse-grained manner via static scopes, the fine-grained, dynamic permissions are handled separately through roles or claims.