Add ComponentFrameworkEndpointMetadata and ConfigureFrameworkEndpoints to identify and configure Blazor infrastructure endpoints

[Copilot]

Problem

When configuring Blazor applications, calling RequireAuthorization() on the component builder affects all endpoints, including internal infrastructure endpoints like _framework/opaque-redirect, _blazor/disconnect, and _blazor/initializers. This creates a painful developer experience where users need to manually find and reconfigure these framework endpoints to exclude them from authorization requirements.

// This affects ALL endpoints, including internal ones
var components = app.MapRazorComponents<App>()
    .RequireAuthorization();

// Users currently have to do painful manual endpoint discovery
components.Finally(builder => 
{
    if (builder.DisplayName == "Blazor disconnect" || 
        builder.DisplayName == "Blazor initializers" ||
        builder.RoutePattern?.RawText?.Contains("opaque-redirect") == true)
    {
        builder.Metadata.Add(new AllowAnonymousAttribute());
    }
});

Solution

This PR introduces ComponentFrameworkEndpointMetadata, a public sealed marker class that identifies Blazor's infrastructure endpoints, and a ConfigureFrameworkEndpoints extension method that provides a clean API for configuring framework endpoints specifically.

New APIs:

namespace Microsoft.AspNetCore.Components.Endpoints;

/// <summary>
/// Metadata that identifies infrastructure endpoints for Blazor framework functionality.
/// This marker is used to distinguish framework endpoints (like opaque redirection, 
/// disconnect, and JavaScript initializers) from regular component endpoints.
/// </summary>
public sealed class ComponentFrameworkEndpointMetadata
{
}

namespace Microsoft.AspNetCore.Builder;

/// <summary>
/// Configures framework endpoints for the Blazor application.
/// </summary>
public static RazorComponentsEndpointConventionBuilder ConfigureFrameworkEndpoints(
    this RazorComponentsEndpointConventionBuilder builder,
    Action<EndpointBuilder> configureEndpoints)

Enhanced Developer Experience:

var components = app.MapRazorComponents<App>()
    .RequireAuthorization();

// Option 1: Using the metadata marker directly
components.Finally(builder => 
{
    if (builder.Metadata.OfType<ComponentFrameworkEndpointMetadata>().Any())
    {
        builder.Metadata.Add(new AllowAnonymousAttribute());
    }
});

// Option 2: Using the new ConfigureFrameworkEndpoints extension method
components.ConfigureFrameworkEndpoints(frameworkEndpoint => 
{
    frameworkEndpoint.Metadata.Add(new AllowAnonymousAttribute());
});

Infrastructure Endpoints Enhanced

The following Blazor framework endpoints now include ComponentFrameworkEndpointMetadata:

• Opaque Redirection (_framework/opaque-redirect) - Used for enhanced navigation redirects
• Blazor Server Disconnect (_blazor/disconnect) - Used for circuit cleanup
• Blazor Server Initializers (_blazor/initializers) - Used for JavaScript initialization
• WebAssembly Framework Files (_framework/*) - Used for serving WebAssembly static assets

Implementation Details

• Minimal Changes: Added metadata only where endpoints are registered, no breaking changes
• Consistent Pattern: All framework endpoints use the same identification mechanism
• Clean API: The ConfigureFrameworkEndpoints extension method provides a simple way to target framework endpoints
• Future-Proof: New framework endpoints can easily adopt this pattern
• Well-Tested: Comprehensive unit tests verify metadata and extension method work correctly

This change provides the "first class support" requested in the issue for targeting framework endpoints without requiring users to understand implementation details or hardcode endpoint patterns.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Blazor] Better way to configure some of the "internal" blazor endpoints</issue_title>
<issue_description>When you do things like call RequireAuthorization on the Blazor builder, all the endpoints start requiring auth, including endpoints like _framework/opaque-redirect or _blazor/initializers.

Reconfiguring these endpoints is "kind of painful" (see code below) because you need to "find the endpoint" and then apply the attribute.

var components = app.MapRazorComponents<App>()
    .AddInteractiveServerRenderMode()
    .RequireAuthorization();

components.Add(e => {
    if(e is RouteEndpointBuilder rb)
    {
        if(rb.RoutePattern!.RawText!.Contains("_blazor")){
            rb.Metadata.Add(new AllowAnonymousAttribute());
        }
    }
});

Ideally, we want to have some level of "first class support" for targeting these endpoints to add conventions to them without the user having to dig the details. Something like ConfigureFrameworkEndpointsMetadata that receives a callback to add metadata to those endpoints (we wouldn't expose stuff that allowed changing routes, etc. Since that's hardcoded in a bunch of places.
</issue_description>

<agent_instructions>Make a list of all the "infrastructure" endpoints registered for a Blazor application, like the disconnect for Blazor Server, the Opaque redirect for enhanced nav and so on.
Create a type in Components.Endpoints we can use while building the set of endpoints to annotate those endpoints. The name can be ComponentFrameworkEndpointMetadata. It should be public and sealed, and contain no parameters or properties. It is only "a marker" to identify these special endpoints. Locate the places in code where we are defining these endpoints and make sure you add the attribute to them.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #57193

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[javiercn]

@copilot I have a few comments.

We also want to have an extension method that allows us to configure the framework endpoints easily.

Maybe ConfigureFrameworkEndpoints(endpointBuilder => ...) that calls Add to add a convention but first checks if the attribute is there before running the callback.

[javiercn]

Remove this test

[Copilot]

Removed the ComponentFrameworkEndpointMetadataTest.cs file. Commit: 1c1c0b9

[javiercn]

There are errors here src/Components/Server/test/ComponentEndpointRouteBuilderExtensionsTest.cs(142,46): error CS1061: (NETCORE_ENGINEERING_TELEMETRY=Build) 'IList' does not contain a definition for 'GetMetadata' and no accessible extension method 'GetMetadata' accepting a first argument of type 'IList' could be found (are you missing a using directive or an assembly reference?)

[Copilot]

Fixed the compilation error by using OfType<ComponentFrameworkEndpointMetadata>().Any() instead of GetMetadata<ComponentFrameworkEndpointMetadata>() on IList<object>. Commit: 1c1c0b9

[Copilot]

@copilot I have a few comments.

We also want to have an extension method that allows us to configure the framework endpoints easily.
...

Added the ConfigureFrameworkEndpoints extension method as requested. It checks for ComponentFrameworkEndpointMetadata before applying the configuration callback, providing a clean API for configuring framework endpoints. Commit: 1c1c0b9