First draft of implementation (#1)

* First draft of implementation

Readme will follow

* Rename id.

* Exclude `commons-io` to disable build warnings

* Simplify metrics and add documentation

src/main/java/io/kokuwa/keycloak/metrics/MicrometerEventListener.java

@@ -0,0 +1,32 @@
+package io.kokuwa.keycloak.metrics;
+
+import org.keycloak.events.Event;
+import org.keycloak.events.EventListenerProvider;
+import org.keycloak.events.admin.AdminEvent;
+
+/**
+ * Listener for {@link Event} and {@link AdminEvent}.
+ *
+ * @author Stephan Schnabel
+ */
+public class MicrometerEventListener implements EventListenerProvider, AutoCloseable {
+
+	private final MicrometerEventRecorder recorder;
+
+	MicrometerEventListener(MicrometerEventRecorder recorder) {
+		this.recorder = recorder;
+	}
+
+	@Override
+	public void onEvent(Event event) {
+		recorder.userEvent(event);
+	}
+
+	@Override
+	public void onEvent(AdminEvent event, boolean includeRepresentation) {
+		recorder.adminEvent(event);
+	}
+
+	@Override
+	public void close() {}
+}

src/main/java/io/kokuwa/keycloak/metrics/MicrometerEventListenerFactory.java

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+package io.kokuwa.keycloak.metrics;
+
+import javax.enterprise.inject.spi.CDI;
+
+import org.keycloak.Config.Scope;
+import org.keycloak.events.EventListenerProvider;
+import org.keycloak.events.EventListenerProviderFactory;
+import org.keycloak.models.KeycloakSession;
+import org.keycloak.models.KeycloakSessionFactory;
+
+import io.micrometer.core.instrument.MeterRegistry;
+
+/**
+ * Factory for {@link MicrometerEventListener}, uses {@link MeterRegistry} from CDI.
+ *
+ * @author Stephan Schnabel
+ */
+public class MicrometerEventListenerFactory implements EventListenerProviderFactory {
+
+	private MicrometerEventRecorder recorder;
+
+	@Override
+	public String getId() {
+		return "metrics-listener";
+	}
+
+	@Override
+	public void init(Scope config) {}
+
+	@Override
+	public void postInit(KeycloakSessionFactory factory) {
+		recorder = new MicrometerEventRecorder(CDI.current().select(MeterRegistry.class).get());
+	}
+
+	@Override
+	public EventListenerProvider create(KeycloakSession session) {
+		return new MicrometerEventListener(recorder);
+	}
+
+	@Override
+	public void close() {}
+}

src/main/java/io/kokuwa/keycloak/metrics/MicrometerEventListenerSpi.java

@@ -0,0 +1,32 @@
+package io.kokuwa.keycloak.metrics;
+
+import org.keycloak.events.EventListenerSpi;
+import org.keycloak.provider.Provider;
+
+/**
+ * Factory for {@link MicrometerEventListener}.
+ *
+ * @author Stephan Schnabel
+ */
+public class MicrometerEventListenerSpi extends EventListenerSpi {
+
+	@Override
+	public boolean isInternal() {
+		return false;
+	}
+
+	@Override
+	public String getName() {
+		return "Micrometer Metrics Provider";
+	}
+
+	@Override
+	public Class<? extends Provider> getProviderClass() {
+		return MicrometerEventListener.class;
+	}
+
+	@Override
+	public Class<MicrometerEventListenerFactory> getProviderFactoryClass() {
+		return MicrometerEventListenerFactory.class;
+	}
+}

src/main/java/io/kokuwa/keycloak/metrics/MicrometerEventRecorder.java

@@ -0,0 +1,51 @@
+package io.kokuwa.keycloak.metrics;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.keycloak.events.Event;
+import org.keycloak.events.admin.AdminEvent;
+
+import io.micrometer.core.instrument.Counter;
+import io.micrometer.core.instrument.MeterRegistry;
+
+/**
+ * Micrometer based recorder for events.
+ *
+ * @author Stephan Schnabel
+ */
+public class MicrometerEventRecorder {
+
+	private final Map<String, Counter> counters = new HashMap<>();
+	private final MeterRegistry registry;
+
+	MicrometerEventRecorder(MeterRegistry registry) {
+		this.registry = registry;
+	}
+
+	void adminEvent(AdminEvent event) {
+		counter("keycloak_event_admin",
+				"realm", toBlankIfNull(event.getRealmId()),
+				"resource", toBlankIfNull(event.getResourceType()),
+				"operation", toBlankIfNull(event.getOperationType()),
+				"error", toBlankIfNull(event.getError()));
+	}
+
+	void userEvent(Event event) {
+		counter("keycloak_event_user",
+				"realm", toBlankIfNull(event.getRealmId()),
+				"type", toBlankIfNull(event.getType()),
+				"client", toBlankIfNull(event.getClientId()),
+				"error", toBlankIfNull(event.getError()));
+	}
+
+	private void counter(String counter, String... tags) {
+		counters.computeIfAbsent(counter + Arrays.toString(tags), string -> registry.counter(counter, tags))
+				.increment();
+	}
+
+	private String toBlankIfNull(Object value) {
+		return value == null ? "" : value.toString();
+	}
+}