grafana: add Grafana on monitoring02 with Kanidm OIDC

Deploy Grafana test instance on monitoring02 with:
- Kanidm OIDC authentication (admins -> Admin role, others -> Viewer)
- PKCE enabled for secure OAuth2 flow (required by Kanidm)
- Declarative datasources for Prometheus and Loki on monitoring01
- Local Caddy for TLS termination via internal ACME CA
- DNS CNAME grafana-test.home.2rjus.net

Terraform changes add OAuth2 client secret and AppRole policies for
kanidm01 and monitoring02.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/grafana/default.nix

@@ -0,0 +1,98 @@
+{ config, pkgs, ... }:
+{
+  services.grafana = {
+    enable = true;
+    settings = {
+      server = {
+        http_addr = "127.0.0.1";
+        http_port = 3000;
+        domain = "grafana-test.home.2rjus.net";
+        root_url = "https://grafana-test.home.2rjus.net/";
+      };
+
+      # Disable anonymous access
+      "auth.anonymous".enabled = false;
+
+      # OIDC authentication via Kanidm
+      "auth.generic_oauth" = {
+        enabled = true;
+        name = "Kanidm";
+        client_id = "grafana";
+        client_secret = "$__file{/run/secrets/grafana-oauth2}";
+        auth_url = "https://auth.home.2rjus.net/ui/oauth2";
+        token_url = "https://auth.home.2rjus.net/oauth2/token";
+        api_url = "https://auth.home.2rjus.net/oauth2/openid/grafana/userinfo";
+        scopes = "openid profile email groups";
+        use_pkce = true;  # Required by Kanidm, more secure
+        # Extract user attributes from userinfo response
+        email_attribute_path = "email";
+        login_attribute_path = "preferred_username";
+        name_attribute_path = "name";
+        # Map admins group to Admin role, everyone else to Viewer
+        role_attribute_path = "contains(groups[*], 'admins') && 'Admin' || 'Viewer'";
+        allow_sign_up = true;
+      };
+    };
+
+    # Declarative datasources pointing to monitoring01
+    provision.datasources.settings = {
+      apiVersion = 1;
+      datasources = [
+        {
+          name = "Prometheus";
+          type = "prometheus";
+          url = "http://monitoring01.home.2rjus.net:9090";
+          isDefault = true;
+          uid = "prometheus";
+        }
+        {
+          name = "Loki";
+          type = "loki";
+          url = "http://monitoring01.home.2rjus.net:3100";
+          uid = "loki";
+        }
+      ];
+    };
+  };
+
+  # Vault secret for OAuth2 client secret
+  vault.secrets.grafana-oauth2 = {
+    secretPath = "services/grafana/oauth2-client-secret";
+    extractKey = "password";
+    services = [ "grafana" ];
+    owner = "grafana";
+    group = "grafana";
+  };
+
+  # Local Caddy for TLS termination
+  services.caddy = {
+    enable = true;
+    package = pkgs.unstable.caddy;
+    configFile = pkgs.writeText "Caddyfile" ''
+      {
+        acme_ca https://vault.home.2rjus.net:8200/v1/pki_int/acme/directory
+        metrics
+      }
+
+      grafana-test.home.2rjus.net {
+        log {
+          output file /var/log/caddy/grafana.log {
+            mode 644
+          }
+        }
+
+        reverse_proxy http://127.0.0.1:3000
+      }
+
+      http://${config.networking.hostName}.home.2rjus.net/metrics {
+        metrics
+      }
+    '';
+  };
+
+  # Expose Caddy metrics for Prometheus
+  homelab.monitoring.scrapeTargets = [{
+    job_name = "caddy";
+    port = 80;
+  }];
+}