# Gateway Configuration

This document describes every option bound under the `MxGateway` configuration
section by `GatewayOptions`.

The gateway binds configuration at startup and validates it with
`GatewayOptionsValidator`. Startup fails before the server listens when required
paths, timeouts, queue sizes, enum values, or protocol values are invalid.

## Configuration Shape

```json
{
  "MxGateway": {
    "Authentication": {
      "Mode": "ApiKey",
      "SqlitePath": "C:\\ProgramData\\MxGateway\\gateway-auth.db",
      "PepperSecretName": "MxGateway:ApiKeyPepper",
      "RunMigrationsOnStartup": true
    },
    "Worker": {
      "ExecutablePath": "src\\ZB.MOM.WW.MxGateway.Worker\\bin\\x86\\Release\\ZB.MOM.WW.MxGateway.Worker.exe",
      "WorkingDirectory": null,
      "RequiredArchitecture": "X86",
      "StartupTimeoutSeconds": 30,
      "StartupProbeRetryAttempts": 3,
      "StartupProbeRetryDelayMilliseconds": 250,
      "PipeConnectAttemptTimeoutMilliseconds": 2000,
      "ShutdownTimeoutSeconds": 10,
      "HeartbeatIntervalSeconds": 5,
      "HeartbeatGraceSeconds": 15,
      "MaxMessageBytes": 16777216
    },
    "Sessions": {
      "DefaultCommandTimeoutSeconds": 30,
      "MaxSessions": 64,
      "MaxPendingCommandsPerSession": 128,
      "DefaultLeaseSeconds": 1800,
      "LeaseSweepIntervalSeconds": 30,
      "AllowMultipleEventSubscribers": false
    },
    "Events": {
      "QueueCapacity": 10000,
      "BackpressurePolicy": "FailFast"
    },
    "Dashboard": {
      "Enabled": true,
      "AllowAnonymousLocalhost": true,
      "RequireHttpsCookie": true,
      "SnapshotIntervalMilliseconds": 1000,
      "RecentFaultLimit": 100,
      "RecentSessionLimit": 200,
      "ShowTagValues": false,
      "GroupToRole": {
        "GwAdmin": "Admin",
        "GwReader": "Viewer"
      }
    },
    "Protocol": {
      "WorkerProtocolVersion": 1,
      "MaxGrpcMessageBytes": 16777216
    },
    "Galaxy": {
      "ConnectionString": "Server=localhost;Database=ZB;Integrated Security=True;TrustServerCertificate=True;Encrypt=False;",
      "CommandTimeoutSeconds": 60,
      "DashboardRefreshIntervalSeconds": 30,
      "PersistSnapshot": true,
      "SnapshotCachePath": "C:\\ProgramData\\MxGateway\\galaxy-snapshot.json"
    },
    "Alarms": {
      "Enabled": false,
      "SubscriptionExpression": "",
      "DefaultArea": "",
      "ReconcileIntervalSeconds": 30
    }
  }
}
```

Environment variables use the normal .NET double-underscore form. For example,
`MxGateway__Sessions__MaxSessions=20` overrides
`MxGateway:Sessions:MaxSessions`.

## Authentication Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Authentication:Mode` | `ApiKey` | Selects public gRPC authentication. Supported values are `ApiKey` and `Disabled`. `Disabled` bypasses API-key verification and is for local development only. |
| `MxGateway:Authentication:SqlitePath` | `C:\ProgramData\MxGateway\gateway-auth.db` | SQLite database path for API-key records and audit rows when API-key authentication is enabled. |
| `MxGateway:Authentication:PepperSecretName` | `MxGateway:ApiKeyPepper` | Configuration key used to read the HMAC pepper for API-key secret hashing. The dashboard effective configuration redacts this value. |
| `MxGateway:Authentication:RunMigrationsOnStartup` | `true` | Runs SQLite auth schema migrations at gateway startup when API-key authentication is enabled. |

When `Mode` is `ApiKey`, `SqlitePath` and `PepperSecretName` must be present.
`SqlitePath` must be a valid filesystem path.

## Worker Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Worker:ExecutablePath` | `src\ZB.MOM.WW.MxGateway.Worker\bin\x86\Release\ZB.MOM.WW.MxGateway.Worker.exe` | Path to the x86 worker executable launched for each gateway session. The path must be valid and point to a `.exe` file. |
| `MxGateway:Worker:WorkingDirectory` | `null` | Optional working directory for the worker process. When set, it must be a valid filesystem path. |
| `MxGateway:Worker:RequiredArchitecture` | `X86` | Required Portable Executable architecture for the worker. Supported values are `X86` and `X64`; MXAccess parity uses `X86`. |
| `MxGateway:Worker:StartupTimeoutSeconds` | `30` | Total startup budget for process launch, startup probe, pipe connect, handshake, and worker readiness. |
| `MxGateway:Worker:StartupProbeRetryAttempts` | `3` | Number of retry attempts for transient worker startup probe failures before pipe connection and handshake continue. |
| `MxGateway:Worker:StartupProbeRetryDelayMilliseconds` | `250` | Delay between transient startup probe retry attempts. |
| `MxGateway:Worker:PipeConnectAttemptTimeoutMilliseconds` | `2000` | Per-attempt timeout used by the worker named-pipe connect retry path. The overall pipe connection still stays under the startup budget. |
| `MxGateway:Worker:ShutdownTimeoutSeconds` | `10` | Grace period for worker shutdown before the gateway treats shutdown as failed and may kill the worker process tree. |
| `MxGateway:Worker:HeartbeatIntervalSeconds` | `5` | Worker heartbeat send interval and gateway heartbeat check cadence input. |
| `MxGateway:Worker:HeartbeatGraceSeconds` | `15` | Maximum age of the last worker heartbeat before the gateway faults the worker. This must be greater than or equal to `HeartbeatIntervalSeconds`. |
| `MxGateway:Worker:MaxMessageBytes` | `16777216` | Maximum worker IPC frame payload size in bytes. The validator allows values from `1024` through `268435456`. |

`StartupProbeRetryAttempts`, `StartupProbeRetryDelayMilliseconds`,
`PipeConnectAttemptTimeoutMilliseconds`, timeout values, heartbeat values, and
`MaxMessageBytes` must be positive. `MaxMessageBytes` is intentionally bounded
to avoid accidental large allocations from malformed or oversized frames.

## Session Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Sessions:DefaultCommandTimeoutSeconds` | `30` | Default timeout used while the gateway waits for a worker command reply when an open-session request does not provide a positive command timeout. |
| `MxGateway:Sessions:MaxSessions` | `64` | Maximum number of concurrently open gateway sessions. Session opens reserve a slot atomically before worker creation. |
| `MxGateway:Sessions:MaxPendingCommandsPerSession` | `128` | Maximum number of pending worker commands for one session. Excess commands fail fast instead of queueing indefinitely. |
| `MxGateway:Sessions:DefaultLeaseSeconds` | `1800` | Initial session lease and refresh duration. Unary client activity extends the lease by this duration. |
| `MxGateway:Sessions:LeaseSweepIntervalSeconds` | `30` | Hosted monitor interval for closing expired leases. Active event-stream subscribers keep a session from expiring while the stream remains attached. |
| `MxGateway:Sessions:AllowMultipleEventSubscribers` | `false` | Controls whether multiple `StreamEvents` subscribers may attach to one session. `true` is rejected until event fan-out is implemented. |

All numeric session options must be greater than zero. The current event stream
implementation supports one active subscriber per session; this preserves event
ordering and avoids competing consumers.

## Event Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Events:QueueCapacity` | `10000` | Capacity for bounded per-session event queues used by the gateway worker event channel and the public gRPC event stream queue. |
| `MxGateway:Events:BackpressurePolicy` | `FailFast` | Event backpressure behavior. `FailFast` faults the session on public stream queue overflow. `DisconnectSubscriber` disconnects only the slow stream. |

`QueueCapacity` must be greater than zero. With `FailFast`, queue overflow
faults the affected worker or session instead of silently dropping MXAccess
events. With `DisconnectSubscriber`, public gRPC stream overflow terminates only
the affected stream while the MXAccess session remains active.

## Dashboard Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Dashboard:Enabled` | `true` | Enables Blazor Server dashboard route mapping. The dashboard mounts at the host root (`/`); there is no separate path-base prefix. |
| `MxGateway:Dashboard:AllowAnonymousLocalhost` | `true` | Allows loopback dashboard requests to bypass the dashboard cookie requirement for local development. Remote requests still require dashboard authentication. |
| `MxGateway:Dashboard:RequireHttpsCookie` | `true` | Sets the dashboard auth cookie's secure policy. `true` keeps `CookieSecurePolicy.Always` — the cookie is only sent over HTTPS, which matches a production HTTPS deployment. Set to `false` for plain-HTTP dev deployments to use `CookieSecurePolicy.SameAsRequest`; the cookie is still flagged Secure on HTTPS requests, but it can round-trip over HTTP. Browsers drop Secure cookies set over HTTP from non-localhost hosts, so leaving this `true` while serving the dashboard over plain HTTP will break login from any remote browser. |
| `MxGateway:Dashboard:CookieName` | `MxGatewayDashboard` | Dashboard auth cookie name. Leave unset (null/blank) to use the default. Override it to give a distinct name to a gateway that shares a hostname with another gateway instance: browser cookies are scoped by host+path but **not** by port, so two instances on the same host would otherwise clobber each other's dashboard session under a shared cookie name. Changing it signs out existing dashboard sessions on next deploy. |
| `MxGateway:Dashboard:SnapshotIntervalMilliseconds` | `1000` | Dashboard snapshot refresh interval used by the snapshot SignalR hub and the pages that subscribe to it. |
| `MxGateway:Dashboard:RecentFaultLimit` | `100` | Maximum number of fault summaries projected into each dashboard snapshot. |
| `MxGateway:Dashboard:RecentSessionLimit` | `200` | Maximum number of session summaries projected into each dashboard snapshot. |
| `MxGateway:Dashboard:ShowTagValues` | `false` | Reserved display control for tag values. The dashboard does not show full tag values by default. |
| `MxGateway:Dashboard:GroupToRole` | _(empty)_ | LDAP group → dashboard role mapping. Keys are LDAP group names (short CN or full DN — leading-RDN match). Values must be `Admin` (read/write, API-key CRUD) or `Viewer` (read-only). A user whose LDAP groups don't intersect this map cannot sign in; with no mapping at all, only the loopback bypass admits anyone. |

`SnapshotIntervalMilliseconds` must be greater than zero. `RecentFaultLimit`
and `RecentSessionLimit` must be greater than or equal to zero.
`GroupToRole` values are validated at startup; invalid role names fail
validation. Emptiness is allowed (a closed deployment that admits no LDAP
users) but practical deployments populate at least one Admin group.

### Authorization policies

Three authorization policies are registered out of these options:

- `MxGateway.Dashboard.Viewer` — gates the Razor component routes. Satisfied by
  either dashboard role (Admin or Viewer), by `AllowAnonymousLocalhost` on
  loopback, or by `Authentication.Mode = Disabled`.
- `MxGateway.Dashboard.Admin` — gates write-capable surfaces (API-key CRUD).
  Satisfied only by the Admin role (same environmental bypasses).
- `MxGateway.Dashboard.HubClients` — attached to the SignalR hubs. Accepts
  either the dashboard cookie scheme or the `MxGateway.Dashboard.HubToken`
  bearer scheme (used by SignalR's WebSocket upgrade path where the HttpOnly
  cookie can't be forwarded).

### SignalR hubs

When the dashboard is enabled, three hubs are mapped under `/hubs/*`:

- `GET /hubs/snapshot` — pushes `DashboardSnapshot` whenever the snapshot
  service produces a new one. Drives every page that inherits
  `DashboardPageBase`; replaces the earlier polling loop.
- `GET /hubs/alarms` — re-broadcasts the `AlarmFeedMessage` stream from the
  central alarm monitor to all connected clients (group `__alarms__`).
- `GET /hubs/events` — per-session MxEvent feed. Clients call
  `SubscribeSession(sessionId)` to join `session:{id}`. Events are mirrored
  from the corresponding gRPC `StreamEvents` call as a fire-and-forget
  side-effect; the dashboard only sees events while a gRPC client is also
  subscribed to that session.

`GET /hubs/token` (cookie-only) mints a 30-minute data-protected bearer
token for the calling user; the Blazor pages use it via
`DashboardHubConnectionFactory` to authenticate the SignalR connection.

## Protocol Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Protocol:WorkerProtocolVersion` | `1` | Worker IPC protocol version expected by the gateway and worker. This must match `GatewayContractInfo.WorkerProtocolVersion`. |
| `MxGateway:Protocol:MaxGrpcMessageBytes` | `16777216` | Public gRPC max send and receive message size in bytes. The same default is used by official clients. The validator allows values from `1024` through `268435456`. |

The protocol option is exposed for diagnostics and explicit deployment
configuration, not for compatibility negotiation. A mismatch fails validation
at startup.

## Galaxy Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Galaxy:ConnectionString` | `Server=localhost;Database=ZB;Integrated Security=True;TrustServerCertificate=True;Encrypt=False;` | SQL Server connection string for the Galaxy Repository (`ZB`) used by the `GalaxyRepository` browse RPCs. Override in production via `MxGateway__Galaxy__ConnectionString`. |
| `MxGateway:Galaxy:CommandTimeoutSeconds` | `60` | Per-command SQL timeout for all Galaxy browse RPCs. |
| `MxGateway:Galaxy:DashboardRefreshIntervalSeconds` | `30` | Interval between background refreshes of the dashboard Galaxy summary cache. SQL is hit at most once per interval regardless of dashboard render rate. |
| `MxGateway:Galaxy:PersistSnapshot` | `true` | Persists the latest successful Galaxy browse dataset to disk. When `true`, the cache reloads that snapshot at startup so clients can still browse last-known data while the Galaxy database is unreachable. The restored data is served with `Stale` status until a live query confirms it. |
| `MxGateway:Galaxy:SnapshotCachePath` | `C:\ProgramData\MxGateway\galaxy-snapshot.json` | File path for the persisted Galaxy browse snapshot. Ignored when `PersistSnapshot` is `false`. The snapshot is written atomically (temp file plus rename). |

See [Galaxy Repository Browse](./GalaxyRepository.md) for the RPC surface and
behavior.

## Alarm Options

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Alarms:Enabled` | `false` | Gates the gateway's always-on central alarm monitor. When `true`, the gateway opens one gateway-owned worker session dedicated to alarms, caches the active-alarm set, and fans it out to every client through the `StreamAlarms` RPC — no client opens its own session to see alarms. |
| `MxGateway:Alarms:SubscriptionExpression` | _(empty)_ | AVEVA alarm-subscription expression the monitor subscribes on startup, in canonical `\\<machine>\Galaxy!<area>` form. The literal `Galaxy` provider is correct regardless of the Galaxy database name. When empty and `Enabled` is `true`, the gateway falls back to `\\<MachineName>\Galaxy!<DefaultArea>` if `DefaultArea` is set. |
| `MxGateway:Alarms:DefaultArea` | _(empty)_ | Area name used to compose a default subscription when `SubscriptionExpression` is empty. If both are empty while `Enabled` is `true`, the monitor faults with a configuration diagnostic. |
| `MxGateway:Alarms:ReconcileIntervalSeconds` | `30` | How often the monitor reconciles its in-process alarm cache against the worker's authoritative active-alarm snapshot, catching transitions the live poll-and-diff feed missed. Floored at 5 seconds. |

The alarm monitor is independent of client sessions: `AcknowledgeAlarm` and
`StreamAlarms` are session-less RPCs served by the monitor.

### Alarm fallback options

The `Fallback` sub-section controls how the alarm feed selects between the
native wnwrap alarm-manager provider and the subtag-monitoring fallback.

| Option | Default | Description |
|--------|---------|-------------|
| `MxGateway:Alarms:Fallback:Mode` | `Auto` | Provider selection mode. `Auto` uses the alarm manager as primary and fails over to subtag monitoring after consecutive COM failures, then fails back automatically. `ForceAlarmManager` disables failover. `ForceSubtag` forces subtag monitoring on from startup. Values are case-insensitive. |
| `MxGateway:Alarms:Fallback:ConsecutiveFailureThreshold` | `3` | Number of consecutive wnwrap COM failures (`COMException` or failure HRESULT from `Subscribe` / `GetXmlCurrentAlarms2`) before the monitor switches to subtag mode. Floored at 1. |
| `MxGateway:Alarms:Fallback:FailbackProbeIntervalSeconds` | `30` | While in subtag mode, how often (in seconds) the monitor probes the wnwrap provider to detect recovery. Floored at 1. |
| `MxGateway:Alarms:Fallback:FailbackStableProbes` | `3` | Number of consecutive clean wnwrap probes required before the monitor switches back to the alarm manager. Floored at 1. |
| `MxGateway:Alarms:Fallback:Discovery:UseGalaxyRepository` | `true` | When `true`, the monitor queries the Galaxy Repository SQL database to build the subtag watch-list for the configured area. |
| `MxGateway:Alarms:Fallback:Discovery:Area` | _(empty)_ | Galaxy area to scope the Repository query to. Falls back to `MxGateway:Alarms:DefaultArea` when empty. Ignored when `UseGalaxyRepository` is `false`. This area is **not** used to compose a Repository-derived alarm's canonical `Galaxy!{area}.{reference}`: each discovered alarm uses its object's real Galaxy area (discovered via `gobject.area_gobject_id`), so the reference's group matches what the native alarmmgr emits. `Discovery:Area` / `DefaultArea` is used as the composition area only for explicit `IncludeAttributes` entries, which carry no discovered area. |
| `MxGateway:Alarms:Fallback:Discovery:IncludeAttributes` | _(empty)_ | Explicit MXAccess attribute paths to add to the subtag watch-list, supplementing (or replacing, when `UseGalaxyRepository` is `false`) the Repository-derived list. |
| `MxGateway:Alarms:Fallback:Discovery:ExcludeAttributes` | _(empty)_ | Attribute paths to remove from the merged watch-list (case-insensitive). The exclude is applied after the Repository-derived rows and the explicit `IncludeAttributes` entries are combined, so an exclude that matches an explicit include suppresses it too — excludes win. Ignored when `UseGalaxyRepository` is `false`. |
| `MxGateway:Alarms:Fallback:Subtags:Active` | `InAlarm` | Subtag name for the in-alarm boolean. Confirmed AVEVA `AlarmExtension` field name. |
| `MxGateway:Alarms:Fallback:Subtags:Acked` | `Acked` | Subtag name for the acknowledged boolean. Confirmed AVEVA `AlarmExtension` field name. |
| `MxGateway:Alarms:Fallback:Subtags:AckComment` | `AckMsg` | Subtag name for the acknowledgement comment write target. Writing this subtag performs the acknowledge in AVEVA. Confirmed AVEVA `AlarmExtension` field name. When empty, the ack-comment write path is disabled. |
| `MxGateway:Alarms:Fallback:Subtags:Priority` | `Priority` | Subtag name for the alarm priority / severity value. Confirmed AVEVA `AlarmExtension` field name. |

Validation rules:

- `Mode` must be `Auto`, `ForceAlarmManager`, or `ForceSubtag` (case-insensitive).
- `Mode = ForceSubtag` with both `UseGalaxyRepository = false` and an empty
  `IncludeAttributes` list produces a startup validation warning: the subtag
  provider has no attributes to advise.
- `ConsecutiveFailureThreshold`, `FailbackProbeIntervalSeconds`, and
  `FailbackStableProbes` are floored at 1 by `GatewayOptionsValidator`.

Full example with non-default fallback settings:

```json
{
  "MxGateway": {
    "Alarms": {
      "Enabled": true,
      "SubscriptionExpression": "\\\\SCADA01\\Galaxy!PlantArea",
      "DefaultArea": "PlantArea",
      "ReconcileIntervalSeconds": 30,
      "Fallback": {
        "Mode": "Auto",
        "ConsecutiveFailureThreshold": 3,
        "FailbackProbeIntervalSeconds": 30,
        "FailbackStableProbes": 3,
        "Discovery": {
          "UseGalaxyRepository": true,
          "Area": "",
          "IncludeAttributes": [],
          "ExcludeAttributes": []
        },
        "Subtags": {
          "Active": "InAlarm",
          "Acked": "Acked",
          "AckComment": "AckMsg",
          "Priority": "Priority"
        }
      }
    }
  }
}
```

The defaults (`InAlarm`/`Acked`/`AckMsg`/`Priority`) are the confirmed AVEVA
`AlarmExtension` primitive field names, verified by querying the live ZB Galaxy
`attribute_definition` rows. The `Subtags` block exists so names can be
overridden without a code change if a site's alarm template uses different
attribute names. See `docs/AlarmClientDiscovery.md` for the synthesis rules that
depend on these names.

## Host Endpoints and Transport Security (Kestrel)

The listening endpoints are **not** part of the `MxGateway` section. The gateway
uses the stock ASP.NET Core host (`WebApplication.CreateBuilder`) with no
`ConfigureKestrel` call in code, so endpoints come entirely from the standard
`Kestrel` configuration section. On the deployed hosts these values are supplied
as NSSM environment variables (`Kestrel__Endpoints__...`), not from
`appsettings.json`.

Two named endpoints are bound:

| Endpoint name | Purpose | Protocol requirement |
|---|---|---|
| `Http` | Public gRPC API (sessions, invoke, events, Galaxy browse) | HTTP/2 |
| `Dashboard` | Blazor dashboard and SignalR hubs | HTTP/1.1 (HTTP/2 optional) |

Both endpoints share one routing pipeline; the names only select which TCP port
serves which traffic. The gRPC endpoint must negotiate **HTTP/2**, which drives
the protocol settings below.

### Plaintext (current deployments)

Both running hosts (`10.100.0.48` and `wonder-app-vd03`) serve the gRPC port in
**cleartext HTTP/2 (`h2c`)**. Because cleartext HTTP/2 has no ALPN to negotiate
the protocol, the gRPC endpoint must be pinned to `Http2` with prior knowledge:

```text
Kestrel__Endpoints__Http__Url=http://0.0.0.0:5120
Kestrel__Endpoints__Http__Protocols=Http2
Kestrel__Endpoints__Dashboard__Url=http://0.0.0.0:5130
```

In this mode all client↔gateway traffic — including the
`authorization: Bearer mxgw_...` API key and any `WriteSecured` / `AuthenticateUser`
payloads — crosses the network **unencrypted**. This is acceptable only on a
trusted/isolated network segment. Prefer TLS for anything else.

### TLS

To encrypt the gRPC channel, give the `Http` endpoint an `https://` URL and a
certificate. Over TLS, ALPN negotiates HTTP/2, so the explicit `Protocols=Http2`
pin is no longer required (the default `Http1AndHttp2` works for gRPC over TLS).

`appsettings.json` form:

```json
{
  "Kestrel": {
    "Endpoints": {
      "Http": {
        "Url": "https://0.0.0.0:5120",
        "Certificate": {
          "Path": "C:\\ProgramData\\MxGateway\\certs\\gateway.pfx",
          "Password": "<pfx-password>"
        }
      },
      "Dashboard": {
        "Url": "https://0.0.0.0:5130",
        "Certificate": {
          "Path": "C:\\ProgramData\\MxGateway\\certs\\gateway.pfx",
          "Password": "<pfx-password>"
        }
      }
    }
  }
}
```

Equivalent NSSM environment-variable form (how config is delivered on the hosts —
see [server deploy mechanics in the project notes]):

```text
Kestrel__Endpoints__Http__Url=https://0.0.0.0:5120
Kestrel__Endpoints__Http__Certificate__Path=C:\ProgramData\MxGateway\certs\gateway.pfx
Kestrel__Endpoints__Http__Certificate__Password=<pfx-password>
Kestrel__Endpoints__Dashboard__Url=https://0.0.0.0:5130
Kestrel__Endpoints__Dashboard__Certificate__Path=C:\ProgramData\MxGateway\certs\gateway.pfx
Kestrel__Endpoints__Dashboard__Certificate__Password=<pfx-password>
```

Certificate sourcing options (any standard ASP.NET Core form is accepted):

| Form | Keys |
|---|---|
| PFX file | `Certificate:Path` (+ `Certificate:Password` if encrypted) |
| PEM pair | `Certificate:Path` (cert) + `Certificate:KeyPath` (private key) |
| Windows cert store | `Certificate:Subject`, `Certificate:Store` (e.g. `My`), `Certificate:Location` (`LocalMachine`), `Certificate:AllowInvalid` |

The certificate's CN/SAN must cover the host name clients dial (or clients must
set a server-name override — see below). The dashboard endpoint can keep its own
certificate independent of the gRPC endpoint; pair this with
`MxGateway:Dashboard:RequireHttpsCookie` (`true`) for production HTTPS.

### Automatic self-signed certificate

`mxaccessgw` is an internal tool with no PKI to issue certificates, so requiring
an operator to supply one before TLS works pushed deployments toward plaintext.
To avoid that, the gateway fills in a self-signed certificate when an HTTPS
endpoint is configured without one.

**Trigger.** At startup the gateway inspects `Kestrel:Endpoints:*`. If any
endpoint has an `https://` URL and no `Certificate` subsection of its own, and no
`Kestrel:Certificates:Default` is set, the gateway generates (or loads) a
persisted self-signed certificate and wires it in as the HTTPS *default* via
`ConfigureHttpsDefaults`. All-plaintext deployments are untouched: when no HTTPS
endpoint is configured, no certificate or key material is generated or written.

**Generated certificate.** ECDSA P-256, `serverAuth` EKU, validity ≈
`ValidityYears` (default 10 years, with one day of clock-skew slack before
`notBefore`). SANs cover `localhost`, the machine name (and its FQDN when
resolvable), each entry in `AdditionalDnsNames`, and the loopback addresses
`127.0.0.1` and `::1`.

**`MxGateway:Tls:*` options.** All optional; the zero-config path needs none of
them.

| Option | Default | Purpose |
|---|---|---|
| `Tls:SelfSignedCertPath` | `C:\ProgramData\MxGateway\certs\gateway-selfsigned.pfx` | Where the generated certificate is persisted |
| `Tls:ValidityYears` | `10` | Lifetime of the generated certificate (validated 1–100) |
| `Tls:AdditionalDnsNames` | `[]` | Extra DNS SANs (e.g. a load-balancer name) |
| `Tls:RegenerateIfExpired` | `true` | Replace an expired persisted certificate instead of failing |

`ValidityYears` is validated by `GatewayOptionsValidator` (range 1–100); the
"HTTPS endpoint configured but no certificate available" fail-fast lives in the
bootstrap/provider, because the validator only sees the `MxGateway` section, not
`Kestrel:Endpoints`.

**Persistence.** The PFX is written with an **empty** export password — a random
in-memory password could not be reused across restarts, which the
persist-and-reuse model requires. The private key is instead protected at rest by
filesystem permissions: a restrictive ACL on Windows (SYSTEM + Administrators,
inherited ACEs stripped) on the `certs` directory and file, and mode `0600` on
non-Windows. The write is atomic (hardened temp file, then move). The persisted
certificate is reused across restarts (stable thumbprint, so CA-pinning clients
keep working) and regenerated only when it is missing, expired (and
`RegenerateIfExpired` is `true`), or unreadable/corrupt. If the directory is not
writable or the ACL cannot be applied, the gateway fails fast with a diagnostic
naming the path rather than falling back to an in-memory certificate.

**Logging.** On generate or load, the gateway logs the certificate thumbprint,
SAN list, and `notAfter` at Information. The PFX bytes, export password, and
private key are never logged.

**Operator override.** The generated certificate is only the HTTPS *default*. To
use a real certificate, configure one explicitly — either per endpoint via
`Kestrel:Endpoints:<name>:Certificate` (`Path`/`Subject`/`Thumbprint`, etc., as
in the table above) or globally via `Kestrel:Certificates:Default`. An
explicitly-configured certificate takes precedence, and the gateway then writes
no self-signed material.

### Client side

Each official client opts into TLS explicitly. For the .NET client
(`MxGatewayClientOptions`):

| Option | Effect |
|---|---|
| `UseTls` (default `false`) | Enables TLS. Requires an `https://` endpoint; an `https://` endpoint without `UseTls` fails validation, and vice versa. |
| `CaCertificatePath` | Pins a custom root (self-signed / private CA) using `CustomRootTrust` chain validation instead of the OS trust store; the .NET client also enforces the certificate hostname/SAN match on this path. |
| `RequireCertificateValidation` (default `false`) | Forces OS/system-trust verification on a TLS connection with no pinned CA. Leave `false` for the lenient default. |
| `ServerNameOverride` | SNI / certificate host name override when the dialed host differs from the certificate CN/SAN. |

To pair with the auto-generated self-signed certificate above, the clients are
**lenient by default**: a TLS connection with no pinned CA accepts whatever
certificate the gateway presents. Pin `CaCertificatePath` to verify, or set
`RequireCertificateValidation` to force system-trust verification without
pinning. The other language clients expose the equivalent options; the exact
behavior differs per stack — Python uses trust-on-first-use and Rust is pin-only.
See each client README for the as-built behavior.

### Gateway↔worker IPC

Transport security here applies only to the public gRPC channel. The
gateway↔worker link is a per-session **named pipe**
(`mxaccess-gateway-{gatewayPid}-{sessionId}`), not a network socket. It is not
TLS-encrypted and does not need to be: it never leaves the local Windows host and
is secured by the OS pipe ACL. See [Worker Frame Protocol](./WorkerFrameProtocol.md).

## Related Documentation

- [Gateway Process Detailed Design](./GatewayProcessDesign.md)
- [Gateway Dashboard Detailed Design](./GatewayDashboardDesign.md)
- [Worker Process Launcher](./WorkerProcessLauncher.md)
- [Worker Frame Protocol](./WorkerFrameProtocol.md)
- [Galaxy Repository Browse](./GalaxyRepository.md)
