Set up Nginx Reverse Proxy for VPC-based Kibana Dashboard That Use AWS Cognito with OKTA for Authentication

Question

I have a system that redirect to a front end application which used AWS Cognito + OKTA to authenticate. Once front end loaded, user have to click on a link to navigate to the Kibana dashboard. The token will be passed to the Kibana dashboard page. However, when I moved the Kibana into a VPC and setup a Nginx reverse proxy to enable the access from outside VPC, the dashboard failed to load. I tried it was working fine when I was used cognito (without OKTA) to access the dashboard. The dashboard is working fine too when I using cognito with OKTA. Because the dashboard manage to show on a browser of an EC2 under the same VPC.