feat: implement GitHub webhook HMAC-SHA256 signature verification

Verify X-Hub-Signature-256 header using CryptoUtil.hmacSha256 from
onixbyte crypto-toolbox. Signature check is skipped when no secret is
configured. Uses MessageDigest.isEqual for constant-time comparison.

build.gradle.kts

@@ -36,6 +36,7 @@ dependencies {
     implementation(libs.onixbyte.identityGenerator)
     implementation(libs.onixbyte.captcha)
     implementation(libs.onixbyte.regions)
+    implementation(libs.onixbyte.cryptoToolbox)
     implementation(libs.jwt.core)
     implementation(libs.spring.boot.configurationProcessor)
     implementation(libs.spring.boot.actuator)

gradle/libs.versions.toml

@@ -31,6 +31,7 @@ jackson-jsr310 = { group = "com.fasterxml.jackson.datatype", name = "jackson-dat
 onixbyte-versionCatalogue = { group = "com.onixbyte", name = "version-catalogue", version.ref = "onixbyteVersion" }
 onixbyte-tuple = { group = "com.onixbyte", name = "tuple" }
 onixbyte-commonToolbox = { group = "com.onixbyte", name = "common-toolbox" }
+onixbyte-cryptoToolbox = { group = "com.onixbyte", name = "crypto-toolbox", version.ref = "onixbyteVersion" }
 onixbyte-mathToolbox = { group = "com.onixbyte", name = "math-toolbox" }
 onixbyte-identityGenerator = { group = "com.onixbyte", name = "identity-generator" }
 onixbyte-captcha = { group = "com.onixbyte", name = "captcha", version.ref = "onixbyteCaptcha" }

src/main/java/com/onixbyte/deltaforceguide/interceptor/GitHubWebhookInterceptor.java

@@ -0,0 +1,85 @@
+package com.onixbyte.deltaforceguide.interceptor;
+
+import com.onixbyte.crypto.util.CryptoUtil;
+import com.onixbyte.deltaforceguide.exeption.BizException;
+import com.onixbyte.deltaforceguide.manager.WebhookManager;
+import com.onixbyte.deltaforceguide.shared.GitHubWebhookHeader;
+import com.onixbyte.deltaforceguide.wrapper.RepeatedlyReadRequestWrapper;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import org.jspecify.annotations.NonNull;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Component;
+import org.springframework.web.servlet.HandlerInterceptor;
+
+import javax.crypto.Mac;
+import javax.crypto.spec.SecretKeySpec;
+import java.nio.charset.StandardCharsets;
+import java.security.InvalidKeyException;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+/**
+ * Verifies GitHub webhook requests by validating the {@code X-Hub-Signature-256}
+ * header against the configured secret using HMAC-SHA256.
+ *
+ * <p>Verification is skipped when no secret is configured. The signature format is
+ * {@code sha256=<hex-digest>} as documented by GitHub.
+ */
+@Component
+public class GitHubWebhookInterceptor implements HandlerInterceptor {
+
+    private static final Logger log = LoggerFactory.getLogger(GitHubWebhookInterceptor.class);
+
+    private final WebhookManager webhookManager;
+
+    public GitHubWebhookInterceptor(WebhookManager webhookManager) {
+        this.webhookManager = webhookManager;
+    }
+
+    @Override
+    public boolean preHandle(
+            @NonNull HttpServletRequest request,
+            @NonNull HttpServletResponse response,
+            @NonNull Object handler
+    ) {
+        if (!(request instanceof RepeatedlyReadRequestWrapper req)) {
+            throw new BizException(HttpStatus.INTERNAL_SERVER_ERROR,
+                    "Request body is not readable");
+        }
+
+        var secret = webhookManager.github().secret();
+        if (secret == null || secret.isBlank()) {
+            log.debug("No GitHub webhook secret configured, skipping signature verification");
+            return true;
+        }
+
+        var signatureHeader = req.getHeader(GitHubWebhookHeader.SIGNATURE_256);
+        if (signatureHeader == null || signatureHeader.isBlank()) {
+            log.warn("Missing {} header from ip={}",
+                    GitHubWebhookHeader.SIGNATURE_256, request.getRemoteAddr());
+            throw new BizException(HttpStatus.UNAUTHORIZED,
+                    "Missing webhook signature header");
+        }
+
+        var body = req.getBodyString();
+        try {
+            var computed = "sha256=" + CryptoUtil.hmacSha256(secret, body);
+
+            if (!MessageDigest.isEqual(
+                    computed.getBytes(StandardCharsets.UTF_8),
+                    signatureHeader.getBytes(StandardCharsets.UTF_8))) {
+                log.warn("Invalid webhook signature from ip={}", request.getRemoteAddr());
+                throw new BizException(HttpStatus.UNAUTHORIZED, "Invalid webhook signature");
+            }
+
+            return true;
+        } catch (NoSuchAlgorithmException | InvalidKeyException e) {
+            log.error("Failed to compute HMAC-SHA256", e);
+            throw new BizException(HttpStatus.INTERNAL_SERVER_ERROR,
+                    "Failed to verify webhook signature");
+        }
+    }
+}