feat(events): add webhook event listener with HMAC signing and retry

CHANGELOG.md

@@ -48,6 +48,7 @@ request adding CHANGELOG notes for breaking (!) changes and possibly other secti
 - Added optional `sessionPolicy` field to `SigV4AuthenticationParameters` for catalog federation. When set, the IAM session policy JSON is attached to the STS AssumeRole request, allowing administrators to restrict vended credentials to only the required AWS services and actions (Principle of Least Privilege).
 - Python CLI: added `--scheme` to specify URL scheme
 - Added opt-in idempotency for `createTable` and `updateTable` in the Iceberg REST catalog. When enabled via `polaris.idempotency.enabled=true` (default `false`), a client-supplied `Idempotency-Key` header is embedded into the table entity and committed in the same transaction as the operation; a retry carrying the same key within the TTL window (`polaris.idempotency.ttl`, default `PT5M`) replays the original success instead of failing — with `AlreadyExists` for `createTable`, or with `CommitFailedException` for `updateTable` when the request's requirements no longer match the already-advanced table.
+- Added a `webhook` event listener (`polaris.event-listener.types=webhook`) that delivers sanitized Polaris events as JSON HTTP POSTs to a configurable endpoint (SIEM/audit collectors). Payloads use a CloudEvents-shaped envelope (`specversion`, `id`, `type`, `source`, original `time`, plus `deliverytime` and CloudEvents-compliant extension attribute names) with optional HMAC-SHA256 signing (`X-Polaris-Signature-256`). Delivery is best-effort and bounded (`max-concurrent`, `max-pending`); transient failures retry with jitter (and `Retry-After` when present); HTTPS is required by default (`require-https`); reserved signature/event headers cannot be overridden by custom headers. Metrics cover success, failure, retries, drops, pending, in-flight, and latency.
 
 ### Changes
 - The admin tool's `bootstrap` command is now idempotent: bootstrapping a realm that is already

bom/build.gradle.kts

@@ -99,6 +99,7 @@ dependencies {
 
     api(project(":polaris-extensions-auth-opa"))
     api(project(":polaris-extensions-auth-ranger"))
+    api(project(":polaris-extensions-events-webhook"))
     api(project(":polaris-extensions-federation-bigquery"))
     api(project(":polaris-extensions-federation-hadoop"))
     api(project(":polaris-extensions-federation-hive"))

extensions/events/webhook/build.gradle.kts

@@ -0,0 +1,52 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+plugins {
+  id("polaris-server")
+  id("org.kordamp.gradle.jandex")
+}
+
+dependencies {
+  implementation(project(":polaris-core"))
+  implementation(project(":polaris-runtime-service"))
+
+  implementation(platform(libs.iceberg.bom))
+  implementation("org.apache.iceberg:iceberg-api")
+
+  implementation(platform(libs.jackson.bom))
+  implementation("com.fasterxml.jackson.core:jackson-databind")
+
+  implementation(platform(libs.quarkus.bom))
+  implementation("io.quarkus:quarkus-core")
+  implementation("io.quarkus:quarkus-jackson")
+  implementation("io.micrometer:micrometer-core")
+  implementation(libs.guava)
+
+  compileOnly(libs.jakarta.enterprise.cdi.api)
+  compileOnly(libs.jakarta.inject.api)
+  compileOnly(libs.jakarta.annotation.api)
+  compileOnly(libs.smallrye.config.core)
+
+  implementation(libs.slf4j.api)
+  implementation(libs.smallrye.common.annotation)
+
+  testImplementation(libs.assertj.core)
+  testImplementation(libs.awaitility)
+  testImplementation(libs.mockito.junit.jupiter)
+}