grafana: log in through keycloak's oidc-client provision

HAL's grafana logged in through a hand-made Keycloak client whose secret sat
in its .env. Requiring oidc-client gives it a client the mesh makes and keeps:
the id and URLs come from the binding, the secret arrives as a file grafana
reads itself (__FILE), and the callback it contributes is what keycloak
registers as its redirect.

GF_SERVER_ROOT_URL is still a literal: a module cannot yet learn the public
name the mesh composes for its own endpoint (hq issue 122), and without it
grafana sends a redirect Keycloak refuses.

modules/grafana/module.json

@@ -47,6 +47,21 @@
       "owner": "472:472",
       "content": "${secret:admin}"
     },
+    {
+      "id": "oidc-secret",
+      "type": "file",
+      "path": "${dir:state}/oidc-client.secret",
+      "mode": "0400",
+      "owner": "472:472",
+      "content": "${secret:oidc-client}"
+    },
+    {
+      "id": "oidc-env",
+      "type": "file",
+      "path": "${dir:state}/oidc.env",
+      "mode": "0644",
+      "content": "GF_SERVER_ROOT_URL=https://grafana.zurag.be\nGF_AUTH_GENERIC_OAUTH_ENABLED=true\nGF_AUTH_GENERIC_OAUTH_NAME=Keycloak\nGF_AUTH_GENERIC_OAUTH_CLIENT_ID=${bound:oidc-client:as}\nGF_AUTH_GENERIC_OAUTH_CLIENT_SECRET__FILE=/run/secrets/oidc-client\nGF_AUTH_GENERIC_OAUTH_SCOPES=openid email profile roles\nGF_AUTH_GENERIC_OAUTH_AUTH_URL=${bound:oidc-client:issuer}${bound:oidc-client:authorization-path}\nGF_AUTH_GENERIC_OAUTH_TOKEN_URL=${bound:oidc-client:issuer}${bound:oidc-client:token-path}\nGF_AUTH_GENERIC_OAUTH_API_URL=${bound:oidc-client:issuer}${bound:oidc-client:userinfo-path}\nGF_AUTH_GENERIC_OAUTH_ROLE_ATTRIBUTE_PATH=contains(roles[*], 'admin') && 'Admin' || contains(realm_access.roles[*], 'admin') && 'Admin' || 'Viewer'\nGF_AUTH_GENERIC_OAUTH_USE_PKCE=true\nGF_AUTH_GENERIC_OAUTH_ALLOW_SIGN_UP=true\nGF_AUTH_GENERIC_OAUTH_ALLOW_ASSIGN_GRAFANA_ADMIN=true\n"
+    },
     {
       "id": "server",
       "type": "container",
@@ -57,11 +72,19 @@
       ],
       "volumes": [
         "${dir:data}:/var/lib/grafana",
-        "${dir:state}/admin.secret:/run/secrets/admin:ro"
+        "${dir:state}/admin.secret:/run/secrets/admin:ro",
+        "${dir:state}/oidc-client.secret:/run/secrets/oidc-client:ro"
       ],
       "env": {
         "GF_SECURITY_ADMIN_PASSWORD__FILE": "/run/secrets/admin"
-      }
+      },
+      "env-file": [
+        "${dir:state}/oidc.env"
+      ],
+      "restart-on": [
+        "oidc-env",
+        "oidc-secret"
+      ]
     },
     {
       "id": "runtime-config",
@@ -92,16 +115,26 @@
     }
   ],
   "requires": [
-    "route"
+    "route",
+    "oidc-client"
   ],
   "contributes": {
     "route": {
       "label": "grafana",
       "endpoint": "web"
+    },
+    "oidc-client": {
+      "label": "grafana",
+      "endpoint": "web",
+      "callback": "/login/generic_oauth"
     }
   },
   "binds": {
-    "route": "${dir:state}/route.json"
+    "route": "${dir:state}/route.json",
+    "oidc-client": "${dir:state}/oidc.json"
+  },
+  "secrets": {
+    "oidc-client": "/var/lib/mesh/grafana/oidc-client"
   },
   "build": {
     "on": [