mxaccessgw/docs/Diagnostics.md

Gateway Diagnostics

The diagnostics subsystem provides structured logging, credential redaction, and request-scoped log enrichment for the gateway. It lives under src/ZB.MOM.WW.MxGateway.Server/Diagnostics/ and is wired into the ASP.NET Core pipeline so every gRPC and HTTP request carries the same correlation fields.

Goals

The subsystem exists to satisfy two security rules from gateway.md: never log passwords or raw credential values for AuthenticateUser, WriteSecured, or related secured operations, and never log full MXAccess values by default. Code paths that touch credentials or tag values must therefore route through GatewayLogRedactor rather than emitting them directly.

A second goal is parity-test diagnosability. Because MXAccess sessions, workers, correlation ids, and command methods are the units of comparison, every log entry produced inside a request scope must carry those identifiers without each call site having to format them.

Log Scopes

GatewayLogScope is a record that captures the fields attached to a logger scope. It only emits keys whose values are non-null, so callers can supply just the identifiers they know about:

public sealed record GatewayLogScope(
    string? SessionId = null,
    int? WorkerProcessId = null,
    ulong? CorrelationId = null,
    string? CommandMethod = null,
    string? ClientIdentity = null)
{
    public IReadOnlyDictionary<string, object?> ToDictionary()
    {
        Dictionary<string, object?> values = [];

        AddIfPresent(values, "SessionId", SessionId);
        AddIfPresent(values, "WorkerProcessId", WorkerProcessId);
        AddIfPresent(values, "CorrelationId", CorrelationId);
        AddIfPresent(values, "CommandMethod", CommandMethod);
        AddIfPresent(values, "ClientIdentity", GatewayLogRedactor.RedactClientIdentity(ClientIdentity));

        return values;
    }

ClientIdentity is passed through GatewayLogRedactor.RedactClientIdentity inside ToDictionary rather than at the call site. This guarantees that any logger scope built from a GatewayLogScope cannot accidentally surface a raw API key, even when a caller forgets to redact before constructing the scope.

How scopes are pushed

GatewayLoggerExtensions exposes a single method that converts a GatewayLogScope into the dictionary form expected by ILogger.BeginScope:

public static class GatewayLoggerExtensions
{
    public static IDisposable? BeginGatewayScope(
        this ILogger logger,
        GatewayLogScope scope)
    {
        ArgumentNullException.ThrowIfNull(logger);
        ArgumentNullException.ThrowIfNull(scope);

        return logger.BeginScope(scope.ToDictionary());
    }
}

The returned IDisposable? follows the standard BeginScope contract: callers wrap it in a using to bound the scope to a request, command, or worker interaction.

Redaction Rules

GatewayLogRedactor centralizes every redaction decision so that policy changes live in one file. Three categories of input are handled differently because each has different "safe to log" prefixes.

Sensitive command methods

A static set names the MXAccess commands that are known to carry credentials in their payloads:

private static readonly HashSet<string> SensitiveCommandMethods = new(StringComparer.OrdinalIgnoreCase)
{
    "AuthenticateUser",
    "WriteSecured",
    "WriteSecured2"
};

public static bool IsCredentialBearingCommand(string? commandMethod)
{
    return commandMethod is not null
        && SensitiveCommandMethods.Contains(commandMethod);
}

The names match the MXAccess command list in gateway.md exactly. Write and Write2 are not in the set because their payloads are tag values, not credentials, and are governed by the valueLoggingEnabled flag described below.

API key redaction

RedactClientIdentity is the single redaction path for identity-bearing values; RedactApiKey is a name-preserving alias for it. Redaction fails closed: the only value that survives with any of its content is a gateway-issued mxgw_<key-id>_<secret> key, whose key id is kept so operators can correlate a log entry to a specific principal.

Input	Output	Why
Bearer mxgw_operator01_super-secret	Bearer mxgw_operator01_[redacted]	Recognized gateway key; key id identifies the principal
Bearer eyJhbGciOi… (any foreign token)	Bearer [redacted]	Structure is unknown, so the whole credential goes
Basic dXNlcjpwYXNz	Basic [redacted]	Same, for any recognized scheme
Bearer mxgw_operator01 (no secret separator)	Bearer mxgw_[redacted]	No trustworthy key-id boundary
Bearer (scheme only), anonymous, some junk	[redacted]	No scheme/credential split that can be trusted
null, "", whitespace	unchanged	Nothing to redact

A scheme word survives only when it is one of the recognized authorization schemes (Bearer, Basic, Digest, Negotiate, NTLM, ApiKey, Token). An unrecognized leading word is as likely to be credential material as it is to be a scheme, so it is dropped along with the rest. The key id is also dropped when it runs longer than 64 characters, which no issued key id does — a long run before the first _ is secret material, not an identifier.

The parse is span-based (no regex, no Split allocation): the value is split once at the first space, and the key id is read up to the first _ of the remainder.

The consequence for callers is that a non-key identity (for example a Windows account name) reaching RedactClientIdentity is now replaced rather than passed through. DashboardRedactor routes only values containing the mxgw_ marker here, so dashboard display names are unaffected.

Command value redaction

Redaction seam wired; value logging still has no opt-in knob (updated 2026-08-07). Since commit 47c0b64 (2026-07-27), RedactCommandValue is wired: GatewayLogRedactorSeam (Diagnostics/GatewayLogRedactorSeam.cs) calls it for any non-null CommandValue log property, gated on CommandMethod, so a command payload that reaches a log event is masked on every sink through the shared ILogRedactor seam. What remains true from the original note: there is still no MxGateway:Diagnostics:LogCommandValues (or equivalent) configuration knob — the seam exposes no opt-in, valueLoggingEnabled is never passed true, so every non-null command value is redacted, credential-bearing or not. In practice no log statement currently emits a CommandValue property, but one that does can no longer leak a payload in the clear.

RedactCommandValue enforces the "values are opt-in and redacted by default" rule:

public static object? RedactCommandValue(
    string? commandMethod,
    object? value,
    bool valueLoggingEnabled = false)
{
    if (value is null)
    {
        return null;
    }

    if (!valueLoggingEnabled || IsCredentialBearingCommand(commandMethod))
    {
        return RedactedValue;
    }

    return value;
}

Two rules combine here. First, when valueLoggingEnabled is false (the default), every value is replaced with [redacted]. Second, even when value logging is enabled, credential-bearing commands still redact. The credential check is therefore unconditional and cannot be overridden by configuration.

The shared RedactedValue constant is "[redacted]". DashboardRedactor reuses it so that gateway logs and dashboard renders use the same placeholder.

Request Logging Middleware

GatewayRequestLoggingMiddlewareExtensions.UseGatewayRequestLoggingScope registers the middleware that pushes a GatewayLogScope for the duration of every request:

public static IApplicationBuilder UseGatewayRequestLoggingScope(this IApplicationBuilder app)
{
    ArgumentNullException.ThrowIfNull(app);

    ILogger logger = app.ApplicationServices
        .GetRequiredService<ILoggerFactory>()
        .CreateLogger("MxGateway.Request");

    return app.Use(async (context, next) =>
    {
        using IDisposable? scope = logger.BeginGatewayScope(new GatewayLogScope(
            SessionId: ReadHeader(context, SessionIdHeaderName),
            WorkerProcessId: ReadInt32Header(context, WorkerProcessIdHeaderName),
            CorrelationId: ReadUInt64Header(context, CorrelationIdHeaderName),
            CommandMethod: ReadHeader(context, CommandMethodHeaderName),
            ClientIdentity: ReadHeader(context, "authorization")));

        await next(context);
    });
}

The scope is keyed off four custom headers and the standard authorization header:

Header	Scope field	Type
x-session-id	SessionId	string
x-worker-process-id	WorkerProcessId	int
x-correlation-id	CorrelationId	ulong
x-command-method	CommandMethod	string
authorization	ClientIdentity	string (redacted)

The numeric headers use int.TryParse and ulong.TryParse; missing or unparseable values become null and are dropped by GatewayLogScope.ToDictionary. This keeps the middleware tolerant of clients that do not yet emit every header, which matters because the earliest call in a session (OpenSession) has no SessionId to send.

The logger category is MxGateway.Request, which lets operators filter the request scope events independently from per-component categories. The logger is resolved once at registration rather than per request: the category is fixed, so a per-request IServiceProvider resolve and ILoggerFactory.CreateLogger (which takes the factory lock) bought nothing. Scope construction itself stays unconditional — gating it on ILogger.IsEnabled would drop scope state for providers and scope consumers registered after startup.

Pipeline ordering

GatewayApplication.Build registers the middleware before authentication, authorization, and endpoint mapping:

app.UseGatewayRequestLoggingScope();
app.UseStaticFiles();
app.UseAuthentication();
app.UseAuthorization();
app.UseAntiforgery();
app.MapGatewayEndpoints();

The order matters: putting the logging scope first ensures that authentication failures, authorization denials, and endpoint exceptions all run inside the request scope, so failure logs still carry the correlation id and session id headers that the caller sent. The ClientIdentity field is redacted before logging, so reading the authorization header at this stage does not leak the bearer secret into authentication failure logs.

Consumers

GatewayLoggerExtensions.BeginGatewayScope is consumed by GatewayRequestLoggingMiddlewareExtensions to attach the per-request scope. Component-level call sites build narrower GatewayLogScope instances (for example, with a known WorkerProcessId after a worker launch) and push a nested scope on top of the request scope.

GatewayLogRedactor is consumed in three places:

• GatewayLogScope.ToDictionary redacts ClientIdentity whenever a scope is materialized.
• DashboardRedactor.Redact delegates to RedactClientIdentity for any value containing the mxgw_ marker, then falls back to a marker-keyword check for fields like password or token. This keeps dashboard renders aligned with log redaction.
• ZB.MOM.WW.MxGateway.Tests/Diagnostics/GatewayLogRedactorTests.cs covers each redaction branch, including the assertion that WriteSecured values stay redacted even when valueLoggingEnabled is true.

Health Checks

The shared ZB.MOM.WW.Health package maps three endpoints — /healthz (live), /health/ready, and /health/active — and each registered check opts into a tier by tag. The gateway registers two:

Check	Endpoint tier	Fails when
auth-store	ready	The SQLite auth store cannot be opened. Every gRPC call authenticates against it, so its reachability genuinely gates whether the process should receive traffic.
mxaccess-sessions	active	Sessions exist and their workers have faulted. Reports total / ready / faulted / starting / closing as entry data.

Zero sessions is Healthy, and the tier choice follows from that. The gateway opens an MXAccess session when a client asks for one and holds none otherwise, so an idle gateway is working normally, not broken. A count threshold ("unhealthy below N") would sit red forever on a host nothing dials yet, and a permanently red probe is one operators stop reading — which leaves them worse off than no probe at all. mxaccess-sessions is therefore graded on whether the sessions that exist are usable:

• nothing faulted → Healthy (including no sessions at all)
• some faulted, some still ready or starting → Degraded
• every session faulted → Unhealthy

For the same reason it is tagged active rather than ready. Readiness decides whether the process should be sent traffic, and a gateway with no sessions is ready to serve; failing readiness there would pull a working gateway out of rotation over a condition its clients create.

Related Documentation

• Identifying A Deployed Build — mapping a running binary back to a commit, and why the InformationalVersion stamp cannot be trusted on Windows builds from 2026-07-09 to 2026-08-10
• Sessions
• gRPC
• Authentication