Add configurable captcha endpoints

src/main/java/com/openisle/service/CaptchaService.java

@@ -0,0 +1,14 @@
+package com.openisle.service;
+
+/**
+ * Abstract service for verifying CAPTCHA tokens.
+ */
+public abstract class CaptchaService {
+    /**
+     * Verify the CAPTCHA token sent from client.
+     *
+     * @param token CAPTCHA token
+     * @return true if token is valid
+     */
+    public abstract boolean verify(String token);
+}

src/main/java/com/openisle/service/RecaptchaService.java

@@ -0,0 +1,35 @@
+package com.openisle.service;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+import java.util.Map;
+
+/**
+ * CaptchaService implementation using Google reCAPTCHA.
+ */
+@Service
+public class RecaptchaService extends CaptchaService {
+
+    @Value("${recaptcha.secret-key:}")
+    private String secretKey;
+
+    private final RestTemplate restTemplate = new RestTemplate();
+
+    @Override
+    public boolean verify(String token) {
+        if (token == null || token.isEmpty()) {
+            return false;
+        }
+        String url = "https://www.google.com/recaptcha/api/siteverify?secret={secret}&response={response}";
+        try {
+            ResponseEntity<Map> resp = restTemplate.postForEntity(url, null, Map.class, secretKey, token);
+            Map body = resp.getBody();
+            return body != null && Boolean.TRUE.equals(body.get("success"));
+        } catch (Exception e) {
+            return false;
+        }
+    }
+}