fix: Update OAuth implementation 6

Author: reeshika-h

src/main/java/com/contentstack/cms/oauth/OAuthHandler.java

@@ -179,6 +179,17 @@ public CompletableFuture<OAuthTokens> exchangeCodeForToken(String code) {
      */
     private void _saveTokens(OAuthTokens tokens) {
         this.tokens = tokens;
+        // Update the client's auth state
+        if (tokens != null && tokens.hasAccessToken()) {
+            this.httpClient = this.httpClient.newBuilder()
+                .addInterceptor(chain -> {
+                    Request request = chain.request().newBuilder()
+                        .header("Authorization", "Bearer " + tokens.getAccessToken())
+                        .build();
+                    return chain.proceed(request);
+                })
+                .build();
+        }
     }
 
     /**

src/main/java/com/contentstack/cms/oauth/OAuthInterceptor.java

@@ -57,7 +57,7 @@ public Response intercept(Chain chain) throws IOException {
         Request.Builder requestBuilder = originalRequest.newBuilder()
             .header("X-User-Agent", Util.defaultUserAgent())
             .header("User-Agent", Util.defaultUserAgent())
-            .header("Content-Type", "application/json")
+            .header("Content-Type", originalRequest.url().toString().contains("/token") ? "application/x-www-form-urlencoded" : "application/json")
             .header("X-Header-EA", earlyAccess != null ? String.join(",", earlyAccess) : "true");
 
         // Get current tokens