[data-plane] Add the caching for OIDC JWT token to tokenprovider

data-plane/core/src/main/java/dev/knative/eventing/kafka/broker/core/oidc/TokenProvider.java

@@ -15,30 +15,51 @@
  */
 package dev.knative.eventing.kafka.broker.core.oidc;
 
+import com.google.common.cache.Cache;
+import com.google.common.cache.CacheBuilder;
 import dev.knative.eventing.kafka.broker.core.NamespacedName;
 import io.fabric8.kubernetes.api.model.authentication.TokenRequest;
 import io.fabric8.kubernetes.api.model.authentication.TokenRequestBuilder;
-import io.fabric8.kubernetes.client.Config;
-import io.fabric8.kubernetes.client.ConfigBuilder;
 import io.fabric8.kubernetes.client.KubernetesClient;
-import io.fabric8.kubernetes.client.KubernetesClientBuilder;
+
+import java.util.concurrent.TimeUnit;
 
 public class TokenProvider {
 
     private final KubernetesClient kubernetesClient;
+    private final Cache<String, String> tokenCache;
+
+    public TokenProvider(KubernetesClient kubernetesClient) {
+        this.kubernetesClient = kubernetesClient;
+
+        this.tokenCache = CacheBuilder.newBuilder()
+                .expireAfterWrite(1, TimeUnit.HOURS) // 1 hour expiration after write
+                .maximumSize(1000)
+                .build();
+    }
+
+    public String getToken(NamespacedName serviceAccount, String audience) {
+        String cacheKey = serviceAccount.namespace() + "/" + serviceAccount.name() + "/" + audience;
+        String token = tokenCache.getIfPresent(cacheKey);
 
-    public TokenProvider() {
-        Config clientConfig = new ConfigBuilder().build();
+        if (token == null) {
+            // If the token is not in the cache, request a new one
+            token = requestToken(serviceAccount, audience);
+
+            // If token is successfully retrieved, cache it
+            if (token != null) {
+                tokenCache.put(cacheKey, token);
+            }
+        }
 
-        kubernetesClient =
-                new KubernetesClientBuilder().withConfig(clientConfig).build();
+        return token;
     }
 
-    public String requestToken(NamespacedName serviceAccount, String audience) {
+    private String requestToken(NamespacedName serviceAccount, String audience) {
         TokenRequest tokenRequest = new TokenRequestBuilder()
                 .withNewSpec()
                 .withAudiences(audience)
-                .withExpirationSeconds(3600L)
+                .withExpirationSeconds(3600L) // 1 hour
                 .endSpec()
                 .build();