# Gateway gRPC Authorization

The authorization subsystem has two layers. The gRPC interceptor enforces the
verb scope required by the RPC. Service-layer constraint checks then narrow
what an authenticated API key can browse, read, or write inside the Galaxy.

## Overview

Authorization runs as a single gRPC server interceptor registered for every call on the gateway. It pulls the authenticated identity for the current request, derives the scope that the request type requires, and either lets the call continue or fails the call with a gRPC status. The pipeline keeps service classes free of cross-cutting checks, which matches the `gateway.md` "thin gRPC layer" rule that service handlers translate between contracts and domain code without owning policy.

The participating types live under `src/MxGateway.Server/Security/Authorization/`:

- `GatewayGrpcAuthorizationInterceptor` runs the authenticate-then-authorize pipeline for unary and server-streaming calls.
- `GatewayGrpcScopeResolver` maps a request message (and, for `MxCommandRequest`, the inner `MxCommandKind`) to the scope string that must be present on the caller.
- `GatewayScopes` exposes the canonical scope constants used by the resolver and any downstream consumer.
- `GatewayRequestIdentityAccessor` and `IGatewayRequestIdentityAccessor` expose the verified identity to handlers and any service code that runs inside the call.
- `IConstraintEnforcer` applies optional API-key constraints against the
  cached Galaxy hierarchy from service bodies.
- `GrpcAuthorizationServiceCollectionExtensions` wires the components into the DI container and the gRPC pipeline.

The `ApiKeyIdentity` consumed here is produced by the authentication layer; see [Authentication](./Authentication.md) for how it is built and how scopes are persisted.

## Why an Interceptor

Centralizing the policy in `GatewayGrpcAuthorizationInterceptor` produces three concrete benefits:

1. Every RPC defined in `MxAccessGatewayService` is covered by construction. A new RPC inherits the check the moment its request type is added to `GatewayGrpcScopeResolver`, instead of relying on each service method to remember to call an authorization helper.
2. Verb-scope policy stays centralized. Request-specific constraints still run
   in service bodies because they need command payloads, item handles, and
   Galaxy metadata that the interceptor should not inspect.
3. Authentication and authorization happen in one place, so the gRPC `Status` mapping is consistent. A failed key check always returns `Unauthenticated`, and a missing scope always returns `PermissionDenied` with the offending scope name.

## Interceptor Flow

`GatewayGrpcAuthorizationInterceptor` overrides both `UnaryServerHandler` and `ServerStreamingServerHandler`. Both call the same private `AuthenticateAndAuthorizeAsync` helper before invoking the continuation, then push the resolved identity onto the accessor for the duration of the call.

```csharp
public override async Task<TResponse> UnaryServerHandler<TRequest, TResponse>(
    TRequest request,
    ServerCallContext context,
    UnaryServerMethod<TRequest, TResponse> continuation)
{
    ApiKeyIdentity? identity = await AuthenticateAndAuthorizeAsync(request, context).ConfigureAwait(false);
    IDisposable? identityScope = identity is null ? null : identityAccessor.Push(identity);
    using (identityScope)
    {
        return await continuation(request, context).ConfigureAwait(false);
    }
}
```

The shared helper performs the actual decision:

```csharp
if (options.Value.Authentication.Mode == AuthenticationMode.Disabled)
{
    return null;
}

string? authorizationHeader = context.RequestHeaders.GetValue("authorization");
ApiKeyVerificationResult verificationResult = await apiKeyVerifier
    .VerifyAsync(authorizationHeader, context.CancellationToken)
    .ConfigureAwait(false);

if (!verificationResult.Succeeded || verificationResult.Identity is null)
{
    throw new RpcException(new Status(
        StatusCode.Unauthenticated,
        "Missing or invalid API key."));
}

string requiredScope = scopeResolver.ResolveRequiredScope(request);
if (!verificationResult.Identity.Scopes.Contains(requiredScope))
{
    throw new RpcException(new Status(
        StatusCode.PermissionDenied,
        $"API key is missing required scope '{requiredScope}'."));
}

return verificationResult.Identity;
```

The flow is:

1. If `GatewayOptions.Authentication.Mode` is `AuthenticationMode.Disabled`, the helper returns `null` immediately. No identity is pushed onto the accessor and the continuation runs without scope enforcement. This matches the `AuthenticationMode` enum, which only defines `ApiKey` and `Disabled`.
2. Otherwise, the `authorization` request header is read directly off `ServerCallContext.RequestHeaders` and handed to `IApiKeyVerifier.VerifyAsync`. A failed verification or a missing identity throws `RpcException` with `StatusCode.Unauthenticated`.
3. `GatewayGrpcScopeResolver.ResolveRequiredScope(request)` produces the scope string. If the identity's `Scopes` set does not contain it, the helper throws `RpcException` with `StatusCode.PermissionDenied` and embeds the missing scope name in `Status.Detail` so callers can diagnose the failure.
4. On success, the verified `ApiKeyIdentity` is returned and pushed onto `IGatewayRequestIdentityAccessor` for the lifetime of the call.

The status codes are deliberately distinct: `Unauthenticated` signals "we do not know who you are," and `PermissionDenied` signals "we know who you are, but you cannot do this." Treating the two as the same code would make troubleshooting harder for client implementations.

## Scope Resolution

`GatewayGrpcScopeResolver` is a stateless singleton that switches on the runtime request type. Top-level RPC requests map directly:

```csharp
public string ResolveRequiredScope(object request)
{
    return request switch
    {
        OpenSessionRequest => GatewayScopes.SessionOpen,
        CloseSessionRequest => GatewayScopes.SessionClose,
        StreamEventsRequest => GatewayScopes.EventsRead,
        MxCommandRequest commandRequest => ResolveCommandScope(commandRequest.Command?.Kind ?? MxCommandKind.Unspecified),
        _ => GatewayScopes.Admin
    };
}
```

The `_ => GatewayScopes.Admin` fallback is intentional: any future request type that the resolver does not recognize fails closed, requiring the strongest scope until the resolver is updated.

`MxCommandRequest` is special because it multiplexes many MxAccess operations through a single RPC. The resolver inspects the embedded `MxCommandKind` so each operation gets its own scope:

```csharp
private static string ResolveCommandScope(MxCommandKind kind)
{
    return kind switch
    {
        MxCommandKind.Write or
        MxCommandKind.Write2 => GatewayScopes.InvokeWrite,

        MxCommandKind.WriteSecured or
        MxCommandKind.WriteSecured2 or
        MxCommandKind.AuthenticateUser => GatewayScopes.InvokeSecure,

        MxCommandKind.ArchestraUserToId or
        MxCommandKind.GetSessionState or
        MxCommandKind.GetWorkerInfo => GatewayScopes.MetadataRead,

        MxCommandKind.DrainEvents => GatewayScopes.EventsRead,
        MxCommandKind.ShutdownWorker => GatewayScopes.Admin,

        _ => GatewayScopes.InvokeRead
    };
}
```

Reads (`Register`, `AddItem`, `Advise`, and any other unspecified kind) fall through to `InvokeRead`, which keeps the matrix small while still separating reads from writes, secured writes, metadata lookups, event drains, and worker shutdown.

## Constraint Enforcement

`ApiKeyIdentity.Constraints` is optional. Empty constraints preserve the
previous behavior: the key is authorized only by its verb scopes. Non-empty
constraints are stored as JSON in `api_keys.constraints` and are applied by
`IConstraintEnforcer` after the interceptor succeeds.

Supported constraints are:

| Constraint | Meaning |
|------------|---------|
| `read_subtrees` | Contained-path globs allowed for read/subscription commands. |
| `write_subtrees` | Contained-path globs allowed for write commands. |
| `read_tag_globs` | Tag-address globs allowed for read/subscription commands. |
| `write_tag_globs` | Tag-address globs allowed for write commands. |
| `max_write_classification` | Maximum Galaxy attribute `security_classification` a key may write. |
| `browse_subtrees` | Contained-path globs used to filter Galaxy browse results and deploy-event counts. |
| `read_alarm_only` | Read/subscription commands must target objects with alarm-bearing attributes. |
| `read_historized_only` | Read/subscription commands must target objects with historized attributes. |

Glob matching is anchored, case-insensitive, and supports `*` and `?`.
Subtree and tag glob lists are alternatives: matching either list allows that
scope dimension. Empty lists mean unconstrained for that dimension.

Constraints are set when a key is created — through the `apikey create-key`
flags (see [Authentication](./Authentication.md)) or the dashboard API Keys
page create dialog (see
[Gateway Dashboard Design](./GatewayDashboardDesign.md#api-keys-page)). The
dashboard API Keys page also renders each key's effective constraints.

The service checks read constraints for `AddItem`, `AddItem2`, `AddItemBulk`,
`SubscribeBulk`, and `AdviseItemBulk`. It checks write constraints for
`Write`, `Write2`, `WriteSecured`, and `WriteSecured2`. Successful item
registrations are tracked per session so later item-handle commands resolve
back to the original tag address. If a constrained key presents an unknown item
handle, the gateway fails closed.

Non-bulk constraint failures return gRPC `PermissionDenied`. Bulk read
commands preserve input order and return a failed `SubscribeResult` for each
denied item while still forwarding allowed items to the worker. Every denial
adds an `api_key_audit` entry with the key id, command kind, target, and
blocking constraint; secured values and raw credentials are never logged.

## Scope Catalog

`GatewayScopes` is the single source of truth for scope strings. Every entry is currently mapped by either the resolver or another security component:

| Constant | Value | Required For |
|----------|-------|--------------|
| `SessionOpen` | `session:open` | `OpenSessionRequest` |
| `SessionClose` | `session:close` | `CloseSessionRequest` |
| `EventsRead` | `events:read` | `StreamEventsRequest`, `MxCommandKind.DrainEvents` |
| `InvokeRead` | `invoke:read` | `MxCommandRequest` for read-style command kinds (`Register`, `AddItem`, `Advise`, and any kind not otherwise mapped) |
| `InvokeWrite` | `invoke:write` | `MxCommandKind.Write`, `MxCommandKind.Write2` |
| `InvokeSecure` | `invoke:secure` | `MxCommandKind.WriteSecured`, `MxCommandKind.WriteSecured2`, `MxCommandKind.AuthenticateUser` |
| `MetadataRead` | `metadata:read` | `MxCommandKind.ArchestraUserToId`, `MxCommandKind.GetSessionState`, `MxCommandKind.GetWorkerInfo`, `GalaxyRepository.TestConnection`, `GalaxyRepository.GetLastDeployTime`, `GalaxyRepository.DiscoverHierarchy`, `GalaxyRepository.WatchDeployEvents` |
| `Admin` | `admin` | `MxCommandKind.ShutdownWorker`, the default for any unrecognized request type, and the dashboard authorization policy |

The `Admin` constant is also referenced by `DashboardAuthenticator` and `DashboardAuthorizationHandler` so that the dashboard and the gRPC layer agree on what "admin" means.

## Identity Access for Downstream Layers

Once authorization passes, `GatewayGrpcAuthorizationInterceptor` calls `identityAccessor.Push(identity)` and disposes the returned scope when the continuation completes. `GatewayRequestIdentityAccessor` stores the active identity in an `AsyncLocal<ApiKeyIdentity?>`, so the value flows across `await` boundaries and child tasks belonging to the same request.

```csharp
public sealed class GatewayRequestIdentityAccessor : IGatewayRequestIdentityAccessor
{
    private readonly AsyncLocal<ApiKeyIdentity?> currentIdentity = new();

    public ApiKeyIdentity? Current => currentIdentity.Value;

    public IDisposable Push(ApiKeyIdentity identity)
    {
        ArgumentNullException.ThrowIfNull(identity);

        ApiKeyIdentity? previousIdentity = currentIdentity.Value;
        currentIdentity.Value = identity;

        return new IdentityScope(this, previousIdentity);
    }
}
```

The returned `IdentityScope` restores the previous value on dispose rather than clearing it. This makes the accessor safe for nested pushes, even though the current interceptor only pushes once per call. Disposing twice is a no-op because of the `disposed` guard inside `IdentityScope`.

Downstream code consumes the accessor through the `IGatewayRequestIdentityAccessor` interface:

```csharp
public interface IGatewayRequestIdentityAccessor
{
    ApiKeyIdentity? Current { get; }

    IDisposable Push(ApiKeyIdentity identity);
}
```

`MxAccessGatewayService` takes `IGatewayRequestIdentityAccessor` as a constructor dependency and reads `Current` whenever it needs to attach the calling identity to a domain operation, which keeps the service free of header parsing or scope checks.

When `AuthenticationMode.Disabled` is configured, no identity is pushed, so `Current` returns `null`. Downstream code must tolerate that, just as it tolerates the absence of a scope check.

## Registration

`GrpcAuthorizationServiceCollectionExtensions.AddGatewayGrpcAuthorization` is the single entry point that registers every component and inserts the interceptor into the gRPC pipeline:

```csharp
public static IServiceCollection AddGatewayGrpcAuthorization(this IServiceCollection services)
{
    services.AddSingleton<GatewayGrpcScopeResolver>();
    services.AddSingleton<IGatewayRequestIdentityAccessor, GatewayRequestIdentityAccessor>();
    services.AddSingleton<GatewayGrpcAuthorizationInterceptor>();
    services.AddGrpc(options => options.Interceptors.Add<GatewayGrpcAuthorizationInterceptor>());

    return services;
}
```

Singleton lifetimes are appropriate because none of the three classes hold per-request state on instance fields; the request-scoped value lives inside the `AsyncLocal` on `GatewayRequestIdentityAccessor`. `GatewayApplication` calls `builder.Services.AddGatewayGrpcAuthorization()` during startup, and the call also performs `AddGrpc`, so the gateway never registers gRPC without the interceptor attached.

## Related Documentation

- [Authentication](./Authentication.md)
- [Gateway Dashboard Design](./GatewayDashboardDesign.md)
- [Grpc](./Grpc.md)
- [GatewayConfiguration](./GatewayConfiguration.md)
- [Galaxy Repository Browse](./GalaxyRepository.md)
