keycloak: provide oidc-client, one mesh-made client per consumer

A module that logs people in through Keycloak had to be given a client by
hand, with its secret copied into the consumer's environment. As a provision
the mesh derives the client id (the consumer's identity, mesh_<node>_<module>)
and mints its secret, and delivers both ends: keycloak creates exactly that
confidential client, the consumer names it through ${bound:oidc-client:as}.

The consumer says where its browser comes back to (`callback`) and which
endpoint it is reached on (`label`/`endpoint`), so the redirect is built from
the same names the mesh composes for its route. keycloak serves the issuer and
the endpoint paths under it; the issuer is the one value an assignment sets,
and the realm is read out of it, so consumer and client cannot disagree.

Only what the mesh made is touched: its clients carry mesh.provisioned=true;
a client of the same id without the mark is refused, never adopted, updated
or deleted. The runtime now gets the admin password as a file, which its
tools also needed and never had.

modules/keycloak/provisioner/index.ts

@@ -0,0 +1,73 @@
+// keycloak's provisioner — the adapter that makes keycloak a provider of the mesh `oidc-client`
+// interface. The reconcile loop, the contributions file and reading the mesh's minted secret are the
+// sdk harness's; this writes only the per-service half: how Keycloak creates, checks and removes a
+// consumer's client (novox/hq ADR 0039/0040/0048). What a client is, and which ones are the mesh's,
+// is in ../oidc.ts.
+//
+// The `oidc-client` interface: a consumer logs people in through the realm this module serves, as
+// the confidential client `as` with the secret the mesh minted, and is redirected back to the
+// callback it contributed under the names the mesh composed for its endpoint. What it is served —
+// the issuer and the endpoint paths under it — is in the manifest's `serves`, settled with the
+// assignment's settings.
+//
+// **The realm is read out of the issuer**, the one value an assignment sets (settings reach both the
+// served facts and this module's config.json): a realm set in one place and an issuer in another
+// would let the consumer be told one realm while its client is made in another.
+
+import { runProvisioner, type Provision } from "@novox/mesh-sdk/provisioner";
+import { emit } from "@novox/mesh-sdk/events";
+import { readFileSync } from "node:fs";
+import { KeycloakClient } from "../client.js";
+import { OidcClients, realmOf } from "../oidc.js";
+
+/** The issuer this assignment serves, from the settings-merged config the mesh delivers. */
+function issuer(): string {
+  const file = process.env.MESH_KEYCLOAK_CONFIG_FILE;
+  let cfg: Record<string, unknown> = {};
+  if (file) {
+    try {
+      cfg = JSON.parse(readFileSync(file, "utf8")) as Record<string, unknown>;
+    } catch {
+      // Absent or unreadable: fall through to the environment, and refuse below if that is empty too.
+    }
+  }
+  const said = typeof cfg.issuer === "string" ? cfg.issuer : process.env.MESH_KEYCLOAK_ISSUER;
+  if (!said) throw new Error("no issuer — the module's config.json carries none and MESH_KEYCLOAK_ISSUER is unset");
+  return said;
+}
+
+const clients = new OidcClients(KeycloakClient.fromEnv(), realmOf(issuer()));
+
+/** Emit a lifecycle event without letting a broker hiccup fail the provisioning itself. */
+async function announce(type: string, body: Record<string, string>): Promise<void> {
+  try {
+    await emit(type, body);
+  } catch (err) {
+    console.error(`[provisioner:oidc-client] emit ${type} failed: ${err}`);
+  }
+}
+
+runProvisioner("oidc-client", {
+  async create(p: Provision): Promise<void> {
+    const done = await clients.ensure(p);
+    if (done === "created") {
+      console.log(`[provisioner:oidc-client] created client ${p.as} in realm ${clients.realm}`);
+      await announce("client.created", { realm: clients.realm, clientId: p.as, consumer: p.consumer ?? "" });
+    }
+  },
+
+  async remove(p: { as: string }): Promise<void> {
+    const done = await clients.remove(p.as);
+    if (done === "not ours") {
+      console.error(`[provisioner:oidc-client] ${p.as}: a client of that id exists that the mesh did not make — left alone`);
+    } else if (done === "removed") {
+      console.log(`[provisioner:oidc-client] removed client ${p.as} from realm ${clients.realm}`);
+    }
+  },
+
+  // Asked every minute by the harness: whether Keycloak still holds this consumer's client exactly as
+  // the mesh gave it, so a client deleted or edited behind the mesh's back is made again (hq issue 120).
+  async holds(p: Provision): Promise<boolean> {
+    return clients.holds(p);
+  },
+});