# gRPC Metadata & Authorization Support - Implementation Plan (DRAFT)

**Status:** Draft (Option 4 Preferred)
**Target:** Q1 2026
**Priority:** High
**Complexity:** Medium

## Overview

Expose gRPC metadata and `ServerCallContext` to handlers, and integrate the existing `ICommandAuthorizationService` and `IQueryAuthorizationService` with gRPC endpoints. This will enable authentication, authorization, distributed tracing, multi-tenancy, and other context-aware features in gRPC services.

## Problem Statement

### Current Limitations

1. **No Authorization in gRPC:**
   - `ICommandAuthorizationService` and `IQueryAuthorizationService` exist but are only used by Minimal API
   - gRPC services skip authorization checks entirely
   - Security gap for gRPC endpoints

2. **No Context Access:**
   - Handlers cannot access `ServerCallContext`
   - Cannot read request metadata (headers, auth tokens, correlation IDs)
   - Cannot set response metadata
   - Cannot access user identity/claims
   - Cannot determine caller information

3. **Authorization Interface Limitation:**
   ```csharp
   Task<AuthorizationResult> IsAllowedAsync(Type commandType, CancellationToken ct);
   ```
   - No access to user context
   - No access to request metadata
   - Cannot implement context-aware authorization

## Goals

1. **Expose Context to Handlers:** Allow handlers to access `ServerCallContext` via accessor service
2. **Integrate Authorization:** Call authorization services before executing handlers in gRPC
3. **Maintain Backward Compatibility:** Existing handlers continue to work without changes
4. **Enable Advanced Scenarios:** Multi-tenancy, distributed tracing, custom authentication
5. **Familiar Pattern:** Use accessor pattern similar to ASP.NET Core's `IHttpContextAccessor`

## Recommended Approach: Context Accessor Pattern (Option 4)

**PREFERRED APPROACH** - Use ambient context accessor similar to `IHttpContextAccessor` in ASP.NET Core.

### Why Option 4?

- ✅ **Zero breaking changes** - No handler interface modifications
- ✅ **Opt-in** - Only inject accessor when context is needed
- ✅ **Familiar pattern** - Mirrors `IHttpContextAccessor` developers already know
- ✅ **Full protocol access** - Can use raw `ServerCallContext` or `HttpContext` features
- ✅ **Flexible** - Handlers that don't need context remain simple

### Implementation Overview

```csharp
// New accessor interface
public interface ICqrsContextAccessor
{
    ServerCallContext? GrpcContext { get; }
    HttpContext? HttpContext { get; }
}

// Handlers opt-in by injecting the accessor
public class AddUserCommandHandler : ICommandHandler<AddUserCommand, int>
{
    private readonly ICqrsContextAccessor _context;

    public AddUserCommandHandler(ICqrsContextAccessor context)
    {
        _context = context;
    }

    public async Task<int> HandleAsync(AddUserCommand command, CancellationToken ct)
    {
        // Access gRPC metadata when available
        if (_context.GrpcContext != null)
        {
            var token = _context.GrpcContext.RequestHeaders.GetValue("authorization");
            var userId = ExtractUserIdFromToken(token);
        }

        // Or access HTTP context when available
        if (_context.HttpContext != null)
        {
            var userId = _context.HttpContext.User?.Identity?.Name;
        }

        // Handler logic...
    }
}
```

See full implementation details in [Option 4 section](#option-4-context-accessor-pattern-ambient-context) below.

---

## Alternative Design Options (For Reference)

### Option 1: Optional ServerCallContext Parameter

**Approach:** Add optional `ServerCallContext` parameter to handler interface methods.

**Handler Interface Changes:**

```csharp
namespace Svrnty.CQRS.Abstractions;

public interface ICommandHandler<TCommand>
{
    Task HandleAsync(TCommand command, CancellationToken cancellationToken = default, ServerCallContext? context = null);
}

public interface ICommandHandler<TCommand, TResult>
{
    Task<TResult> HandleAsync(TCommand command, CancellationToken cancellationToken = default, ServerCallContext? context = null);
}

public interface IQueryHandler<TQuery, TResult>
{
    Task<TResult> HandleAsync(TQuery query, CancellationToken cancellationToken = default, ServerCallContext? context = null);
}
```

**Pros:**
- ✅ Simple and straightforward
- ✅ Backward compatible (optional parameter with default null)
- ✅ Handlers can explicitly access context when needed
- ✅ No dependency on HTTP types in core abstractions

**Cons:**
- ❌ Couples abstractions to gRPC (requires `Grpc.Core` reference)
- ❌ Minimal API handlers won't have access to `HttpContext` through same parameter
- ❌ Different context types for HTTP vs gRPC

**Authorization Service Changes:**

```csharp
namespace Svrnty.CQRS.Abstractions.Security;

public interface ICommandAuthorizationService
{
    Task<AuthorizationResult> IsAllowedAsync(Type commandType, object? context, CancellationToken ct = default);
}
```

Where `context` is:
- `ServerCallContext` for gRPC
- `HttpContext` for Minimal API
- `null` if no context available

---

### Option 2: Unified Context Abstraction

**Approach:** Create abstraction over both `ServerCallContext` and `HttpContext`.

**New Abstraction:**

```csharp
namespace Svrnty.CQRS.Abstractions;

public interface IRequestContext
{
    string? GetHeader(string name);
    void SetHeader(string name, string value);
    IDictionary<string, object> Items { get; }
    CancellationToken CancellationToken { get; }
    IUserContext? User { get; }
}

public interface IUserContext
{
    bool IsAuthenticated { get; }
    string? UserId { get; }
    IEnumerable<string> Roles { get; }
    IEnumerable<Claim> Claims { get; }
}

public interface ICommandHandler<TCommand>
{
    Task HandleAsync(TCommand command, IRequestContext? context = null, CancellationToken ct = default);
}
```

**Implementation Wrappers:**

```csharp
internal class GrpcRequestContext : IRequestContext
{
    private readonly ServerCallContext _grpcContext;

    public GrpcRequestContext(ServerCallContext context)
    {
        _grpcContext = context;
    }

    public string? GetHeader(string name) => _grpcContext.RequestHeaders.GetValue(name);
    public CancellationToken CancellationToken => _grpcContext.CancellationToken;
    // ... map other properties
}

internal class HttpRequestContext : IRequestContext
{
    private readonly HttpContext _httpContext;
    // ... similar mapping
}
```

**Pros:**
- ✅ Protocol-agnostic handlers
- ✅ Unified authorization interface
- ✅ No coupling to gRPC or HTTP in abstractions
- ✅ Can support future protocols (WebSockets, etc.)

**Cons:**
- ❌ Additional abstraction layer (more complexity)
- ❌ Cannot access protocol-specific features (e.g., gRPC deadlines, HTTP response codes)
- ❌ Mapping overhead between contexts
- ❌ Leaky abstraction if protocol-specific needs arise

---

### Option 3: Separate gRPC-Aware Handler Interfaces

**Approach:** Keep existing handlers unchanged, add new gRPC-specific interfaces.

**New Interfaces:**

```csharp
namespace Svrnty.CQRS.Grpc.Abstractions;

public interface IGrpcCommandHandler<TCommand>
{
    Task HandleAsync(TCommand command, ServerCallContext context, CancellationToken ct = default);
}

public interface IGrpcCommandHandler<TCommand, TResult>
{
    Task<TResult> HandleAsync(TCommand command, ServerCallContext context, CancellationToken ct = default);
}

public interface IGrpcQueryHandler<TQuery, TResult>
{
    Task<TResult> HandleAsync(TQuery query, ServerCallContext context, CancellationToken ct = default);
}
```

**Pros:**
- ✅ No changes to core abstractions
- ✅ Explicit opt-in for context access
- ✅ Can access full `ServerCallContext` API
- ✅ Clear separation between gRPC and HTTP handlers

**Cons:**
- ❌ Handler duplication (need to implement both interfaces if supporting HTTP + gRPC)
- ❌ Discovery system needs to handle multiple handler types
- ❌ More complex registration (which handler for which protocol?)

---

### Option 4: Context Accessor Pattern (Ambient Context)

**Approach:** Use service locator/accessor pattern for context access.

**Implementation:**

```csharp
namespace Svrnty.CQRS.Abstractions;

public interface ICommandContextAccessor
{
    ServerCallContext? GrpcContext { get; }
    HttpContext? HttpContext { get; }
}

public class MyCommandHandler : ICommandHandler<MyCommand>
{
    private readonly ICommandContextAccessor _contextAccessor;

    public MyCommandHandler(ICommandContextAccessor contextAccessor)
    {
        _contextAccessor = contextAccessor;
    }

    public async Task HandleAsync(MyCommand command, CancellationToken ct)
    {
        var grpcContext = _contextAccessor.GrpcContext;
        if (grpcContext != null)
        {
            // Access gRPC-specific features
        }
    }
}
```

**Pros:**
- ✅ No changes to handler interfaces
- ✅ Fully backward compatible
- ✅ Handlers can access context only when needed

**Cons:**
- ❌ Ambient context is an anti-pattern (hidden dependency)
- ❌ Harder to test (need to mock accessor)
- ❌ AsyncLocal overhead for context flow
- ❌ Not explicit in handler signature

---

## Authorization Integration

Regardless of which option is chosen, authorization needs to be integrated into the gRPC source generator.

### Source Generator Changes

**File:** `Svrnty.CQRS.Grpc.Generators/ServiceImplementationGenerator.cs`

```csharp
public override async Task<AddUserResponse> AddUser(
    AddUserRequest request,
    ServerCallContext context)
{
    var command = new AddUserCommand
    {
        Name = request.Name,
        Email = request.Email
    };

    // AUTHORIZATION CHECK
    var authService = _serviceProvider.GetService<ICommandAuthorizationService>();
    if (authService != null)
    {
        var authResult = await authService.IsAllowedAsync(typeof(AddUserCommand), context, context.CancellationToken);

        if (authResult == AuthorizationResult.Unauthorized)
        {
            throw new RpcException(new Status(StatusCode.Unauthenticated, "Authentication required"));
        }

        if (authResult == AuthorizationResult.Forbidden)
        {
            throw new RpcException(new Status(StatusCode.PermissionDenied, "Insufficient permissions"));
        }
    }

    // Validation (existing)
    var validator = _serviceProvider.GetService<IValidator<AddUserCommand>>();
    if (validator != null)
    {
        var validationResult = await validator.ValidateAsync(command, context.CancellationToken);
        if (!validationResult.IsValid)
        {
            // ... existing validation error handling
        }
    }

    // Execute handler
    var handler = _serviceProvider.GetRequiredService<ICommandHandler<AddUserCommand, int>>();
    var result = await handler.HandleAsync(command, context.CancellationToken, context); // Option 1

    return new AddUserResponse { Result = result };
}
```

### Authorization Service Update

**Current Interface:**
```csharp
public interface ICommandAuthorizationService
{
    Task<AuthorizationResult> IsAllowedAsync(Type commandType, CancellationToken ct = default);
}
```

**Proposed Interface:**

```csharp
public interface ICommandAuthorizationService
{
    Task<AuthorizationResult> IsAllowedAsync(
        Type commandType,
        object? requestContext = null,
        CancellationToken ct = default);
}
```

Where `requestContext` can be:
- `ServerCallContext` for gRPC
- `HttpContext` for HTTP
- Custom context for other scenarios
- `null` if no context

**Breaking Change Mitigation:**

Add new method with default parameter to maintain backward compatibility:

```csharp
public interface ICommandAuthorizationService
{
    // Old method (deprecated but still supported)
    Task<AuthorizationResult> IsAllowedAsync(Type commandType, CancellationToken ct = default);

    // New method with context
    Task<AuthorizationResult> IsAllowedAsync(Type commandType, object? requestContext, CancellationToken ct = default);
}
```

Default implementation:
```csharp
public abstract class CommandAuthorizationServiceBase : ICommandAuthorizationService
{
    public virtual Task<AuthorizationResult> IsAllowedAsync(Type commandType, CancellationToken ct = default)
    {
        return IsAllowedAsync(commandType, null, ct);
    }

    public abstract Task<AuthorizationResult> IsAllowedAsync(Type commandType, object? requestContext, CancellationToken ct);
}
```

---

## Implementation Phases

### Phase 1: Context Access (Choose Design Option)
- [ ] Decide on design option (1, 2, 3, or 4)
- [ ] Update handler interfaces (if needed)
- [ ] Update source generator to pass context to handlers
- [ ] Create context wrappers/abstractions (if needed)
- [ ] Update Minimal API to work with new approach

### Phase 2: Authorization Service Update
- [ ] Update `ICommandAuthorizationService` and `IQueryAuthorizationService` interfaces
- [ ] Provide backward-compatible base class
- [ ] Update Minimal API to pass context to authorization services

### Phase 3: gRPC Authorization Integration
- [ ] Update source generator to call authorization services
- [ ] Map authorization results to gRPC status codes
- [ ] Handle `Unauthenticated` (401) → `StatusCode.Unauthenticated`
- [ ] Handle `Forbidden` (403) → `StatusCode.PermissionDenied`

### Phase 4: Sample Implementation
- [ ] Create sample authorization service implementation
- [ ] Demonstrate JWT token validation in gRPC
- [ ] Demonstrate role-based authorization
- [ ] Update sample project with authorization examples

### Phase 5: Documentation
- [ ] Update CLAUDE.md with authorization details
- [ ] Document how to implement custom authorization services
- [ ] Document how to access context in handlers
- [ ] Create migration guide

---

## Open Questions

### 1. Which design option should we use?
**Question:** Option 1 (optional parameter), Option 2 (unified abstraction), Option 3 (separate interfaces), or Option 4 (accessor pattern)?

**Decision:** ✅ **Option 4 (Context Accessor Pattern)** - Chosen for backward compatibility and familiar ASP.NET Core pattern.

### 2. Should we support accessing HttpContext in handlers?
**Question:** If a handler wants to access HTTP-specific features, should we support that through the same mechanism?

**Decision:** ✅ **Yes** - `ICqrsContextAccessor` will expose both `GrpcContext` and `HttpContext` properties. Handlers can check which is non-null to determine the protocol.

### 3. Breaking changes to authorization interface?
**Question:** Is it acceptable to add a parameter to the authorization interface?

**Options:**
- Add new method, keep old one (backward compatible but verbose)
- Add optional parameter with default `null` (semi-breaking for implementations)
- Create v2 interfaces (`ICommandAuthorizationServiceV2`)

### 4. How should we handle multi-protocol handlers?
**Question:** If a handler is used by both HTTP and gRPC, how does it differentiate?

**Decision:** ✅ **Check which context is non-null** - Simple null check: `if (_context.GrpcContext != null)` vs `if (_context.HttpContext != null)`

### 5. Should metadata access be strongly typed?
**Question:** Should we provide typed accessors for common metadata (JWT, correlation ID, etc.)?

**Options:**
- Raw string access only: `context.GetHeader("authorization")`
- Typed extensions: `context.GetAuthorizationToken()`, `context.GetCorrelationId()`
- Dedicated metadata services

---

## Success Criteria

### Functional Requirements
- ✅ Handlers can access `ServerCallContext` when needed
- ✅ Authorization services are called before gRPC handler execution
- ✅ Authorization failures return appropriate gRPC status codes
- ✅ Backward compatibility maintained for existing handlers
- ✅ Works with both HTTP and gRPC (if unified approach)

### Security Requirements
- ✅ Unauthorized requests return `StatusCode.Unauthenticated`
- ✅ Forbidden requests return `StatusCode.PermissionDenied`
- ✅ Authorization decisions can access user context
- ✅ JWT tokens can be validated from gRPC metadata

### Performance Requirements
- ✅ Minimal overhead for context passing
- ✅ No performance regression for handlers that don't use context

---

## Migration & Backward Compatibility

### Breaking Changes

**With Option 4:** ✅ **NO BREAKING CHANGES**

- Handler interfaces remain unchanged
- Existing handlers work without modification
- Authorization interface adds optional parameter (backward compatible)

### Migration Path

**For Option 4 (Chosen):**
1. Update to new version
2. All existing handlers continue to work unchanged
3. Handlers that need context inject `ICqrsContextAccessor` via constructor
4. Authorization service implementations can optionally use the new context parameter
5. No code changes required for basic upgrade

---

## Dependencies

### NuGet Packages
- `Grpc.AspNetCore` >= 2.68.0 (already referenced)
- `Microsoft.AspNetCore.Http.Abstractions` (for `HttpContext`, if using unified abstraction)

### Internal Dependencies
- `Svrnty.CQRS.Abstractions` (handler interfaces, authorization interfaces)
- `Svrnty.CQRS.Grpc` (context wrappers, if needed)
- `Svrnty.CQRS.Grpc.Generators` (source generator updates)
- `Svrnty.CQRS.MinimalApi` (authorization integration updates)

---

## Final Recommended Approach

Based on preference for **Option 4 (Context Accessor Pattern)**:

### Implementation Summary

1. **Create `ICqrsContextAccessor` interface:**
   ```csharp
   public interface ICqrsContextAccessor
   {
       ServerCallContext? GrpcContext { get; }
       HttpContext? HttpContext { get; }
   }
   ```

2. **Implement accessor with AsyncLocal:**
   - Use `AsyncLocal<T>` to flow context through async calls
   - Similar to ASP.NET Core's `IHttpContextAccessor` implementation
   - Set context in gRPC interceptor and HTTP middleware

3. **Update authorization interface** with context parameter:
   ```csharp
   Task<AuthorizationResult> IsAllowedAsync(
       Type commandType,
       object? requestContext = null,
       CancellationToken ct = default);
   ```

4. **Update source generator** to:
   - Set context in accessor before calling handler
   - Call authorization service with `ServerCallContext`
   - Map authorization results to gRPC status codes

5. **Provide sample implementations** for:
   - JWT token validation from gRPC metadata
   - Role-based authorization
   - Multi-tenancy with tenant ID from headers
   - Correlation ID extraction and propagation

### Advantages

- ✅ **Zero breaking changes** - No handler signature modifications required
- ✅ **Familiar to ASP.NET Core developers** - Same pattern as `IHttpContextAccessor`
- ✅ **Opt-in complexity** - Simple handlers remain simple
- ✅ **Full protocol support** - Access raw gRPC and HTTP contexts
- ✅ **Testable** - Can mock `ICqrsContextAccessor` in tests

### Next Steps

1. Finalize accessor interface design
2. Implement AsyncLocal-based accessor
3. Update source generator for context setting
4. Integrate authorization checks
5. Create comprehensive samples

---

**Document Version:** 0.2 (DRAFT - Option 4 Selected)
**Last Updated:** 2025-01-08
**Author:** Svrnty Team
**Status:** Ready for Implementation Planning