Add option to enable authentication using Bearer tokens

By enabling the `bearerEnabled` setting, authentication on the
metrics endpoint using valid Bearer tokens can now be enforced.
A client requesting the metrics endpoint must set the
`Authorization: Bearer` header with a valid token obtained from
Keycloak. The token must originate from the realm configured by
the `realm` setting (defaults to `master`) and must have the
role configured in the `role` setting (defaults to `prometheus-metrics`).

Author: sirkrypt0

README.md

@@ -11,6 +11,8 @@ Two distinct providers are defined:
 
 The endpoint is available under `<base url>/realms/<realm>/metrics` (Quarkus). 
 It will return data for all realms, no matter which realm you use in the URL.
+By default, the metrics endpoint is **unprotected** and can be queried by everyone.
+See [External Access](#external-access) to protect your metrics endpoint.
 
 ## License 
 
@@ -433,7 +435,33 @@ keycloak_request_duration_sum{code="200",method="GET",resource="admin,admin/real
 
 ## External Access
 
-To disable metrics being externally accessible to a cluster. Set the environment variable 'DISABLE_EXTERNAL_ACCESS'. Once set enable the header 'X-Forwarded-Host' on your proxy. This is enabled by default on HA Proxy on Openshift.
+By default, the metrics endpoint is **unprotected** and can be queried by everyone.
+You should consider enabling one of the following settings.
+
+#### Bearer Token (recommended)
+
+You can configure authorization on the metrics endpoint using standard Bearer token authentication via the following environment variables (or corresponding CLI arguments).
+
+Environment Variable | Default | Description
+---|---|---
+`KC_SPI_REALM_RESTAPI_EXTENSION_METRICS_BEARER_ENABLED` | `false` | Set to `true` to require a valid Bearer token from a user in the configured realm which has the configured role assigned.
+`KC_SPI_REALM_RESTAPI_EXTENSION_METRICS_REALM` | `master` | Realm of the requesting user.
+`KC_SPI_REALM_RESTAPI_EXTENSION_METRICS_ROLE` | `prometheus-metrics` | Role that the requesting user must have to be able to query the metrics.
+
+To configure your Prometheus instance to obtain an OAuth2 token before querying the metrics endpoint, consult the [official Prometheus OAuth2 configuration](https://prometheus.io/docs/prometheus/latest/configuration/configuration/#oauth2).
+In Keycloak, use a client of type `confidential` that has `Service Accounts Enabled` set to `ON`.
+Then, make sure to include the role configured above in the `Service Account Roles` of that client.
+
+#### Presence of the `X-Forwarded-Host` HTTP header
+
+**Note**: The following requires careful setup of your reverse proxy headers. Please consider [Bearer authentication](#bearer-authentication-recommended) first.
+
+To deny requests which have the `X-Forwarded-Host` header set, set the `DISABLE_EXTERNAL_ACCESS` environment variable to `true`.
+Then, configure your reverse proxy to set the `X-Forwarded-Host` header (which is enabled by default on HA Proxy on Openshift).
+
+Only requests which **don't** have the `X-Forwarded-Host` header set will be able to access the metrics.
+If you configured your proxy correctly to set this by default, all requests going through that proxy won't have access to the metrics.
+Instead, you'll need to access the metrics endpoint e.g. via the internal IP of the Keycloak host (since this won't have the `X-Forwarded-Host` header set).
 
 ## Grafana Dashboard
 

src/main/java/org/jboss/aerogear/keycloak/metrics/MetricsEndpoint.java

@@ -2,20 +2,51 @@
 
 import jakarta.ws.rs.GET;
 import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.ForbiddenException;
+import jakarta.ws.rs.NotAuthorizedException;
 import jakarta.ws.rs.core.Context;
 import jakarta.ws.rs.core.HttpHeaders;
 import jakarta.ws.rs.core.MediaType;
 import jakarta.ws.rs.core.Response;
-import jakarta.ws.rs.core.Response.Status;
 import jakarta.ws.rs.core.StreamingOutput;
+
+import org.jboss.logging.Logger;
+
+import org.keycloak.models.KeycloakSession;
+import org.keycloak.models.RealmModel;
 import org.keycloak.services.resource.RealmResourceProvider;
+import org.keycloak.services.managers.AppAuthManager.BearerTokenAuthenticator;
+import org.keycloak.services.managers.AuthenticationManager.AuthResult;
 
 public class MetricsEndpoint implements RealmResourceProvider {
 
     // The ID of the provider is also used as the name of the endpoint
     public final static String ID = "metrics";
 
-    private static final boolean DISABLE_EXTERNAL_ACCESS = Boolean.parseBoolean(System.getenv("DISABLE_EXTERNAL_ACCESS"));
+    private static final boolean DISABLE_EXTERNAL_ACCESS = Boolean
+            .parseBoolean(System.getenv("DISABLE_EXTERNAL_ACCESS"));
+
+    private final static Logger logger = Logger.getLogger(MetricsEndpoint.class);
+
+    private final Boolean bearerEnabled;
+    private String bearerRole;
+    private AuthResult bearerTokenAuth;
+
+    public MetricsEndpoint(KeycloakSession session, Boolean bearerEnabled, String bearerRealm, String bearerRole) {
+        super();
+
+        this.bearerEnabled = bearerEnabled;
+        if (this.bearerEnabled) {
+            RealmModel realmModel = session.realms().getRealmByName(bearerRealm);
+            if (realmModel == null) {
+                logger.errorf("Could not find realm with name %s", bearerRealm);
+                return;
+            }
+            session.getContext().setRealm(realmModel);
+            this.bearerTokenAuth = new BearerTokenAuthenticator(session).authenticate();
+            this.bearerRole = bearerRole;
+        }
+    }
 
     @Override
     public Object getResource() {
@@ -25,15 +56,28 @@ public Object getResource() {
     @GET
     @Produces(MediaType.TEXT_PLAIN)
     public Response get(@Context HttpHeaders headers) {
+        checkAuthentication(headers);
+
+        final StreamingOutput stream = output -> PrometheusExporter.instance().export(output);
+        return Response.ok(stream).build();
+    }
+
+    private void checkAuthentication(HttpHeaders headers) {
         if (DISABLE_EXTERNAL_ACCESS) {
             if (!headers.getRequestHeader("x-forwarded-host").isEmpty()) {
                 // Request is being forwarded by HA Proxy on Openshift
-                return Response.status(Status.FORBIDDEN).build(); //(stream).build();
+                throw new ForbiddenException("X-Forwarded-Host header is present");
             }
         }
 
-        final StreamingOutput stream = output -> PrometheusExporter.instance().export(output);
-        return Response.ok(stream).build();
+        if (this.bearerEnabled) {
+            if (this.bearerTokenAuth == null) {
+                throw new NotAuthorizedException("Invalid bearer token");
+            } else if (this.bearerTokenAuth.getToken().getRealmAccess() == null
+                    || !this.bearerTokenAuth.getToken().getRealmAccess().isUserInRole(this.bearerRole)) {
+                throw new ForbiddenException("Missing required realm role");
+            }
+        }
     }
 
     @Override

src/main/java/org/jboss/aerogear/keycloak/metrics/MetricsEndpointFactory.java

@@ -8,14 +8,26 @@
 
 public class MetricsEndpointFactory implements RealmResourceProviderFactory {
 
+    private static final String BEARER_ENABLED_CONFIGURATION = "bearerEnabled";
+    private static final String BEARER_REALM_CONFIGURATION = "realm";
+    private static final String DEFAULT_BEARER_REALM = "master";
+    private static final String BEARER_ROLE_CONFIGURATION = "role";
+    private static final String DEFAULT_BEARER_ROLE = "prometheus-metrics";
+
+    private Boolean bearerEnabled;
+    private String bearerRealm;
+    private String bearerRole;
+
     @Override
     public RealmResourceProvider create(KeycloakSession session) {
-        return new MetricsEndpoint();
+        return new MetricsEndpoint(session, this.bearerEnabled, this.bearerRealm, this.bearerRole);
     }
 
     @Override
     public void init(Config.Scope config) {
-        // nothing to do
+        this.bearerEnabled = config.getBoolean(BEARER_ENABLED_CONFIGURATION, false);
+        this.bearerRealm = config.get(BEARER_REALM_CONFIGURATION, DEFAULT_BEARER_REALM);
+        this.bearerRole = config.get(BEARER_ROLE_CONFIGURATION, DEFAULT_BEARER_ROLE);
     }
 
     @Override