A company has several workloads running on AWS. Employees are required to authenticate using on-premises ADFS and SSO to access the AWS Management Console. Developers migrated an existing legacy web application to an Amazon EC2 instance. Employees need to access this application from anywhere on the internet, but currently, there is no authentication system built into the application.
How should the Security Engineer implement employee-only access to this system without changing the application?

A. Place the application behind an Application Load Balancer (ALB). Use Amazon Cognito as authentication for the ALB. Define a SAML based Amazon Cognito user pool and connect it to ADFS.
B. Implement AWS SSO in the master account and link it to ADFS as an identity provider. Define the EC2 instance as a managed resource, then apply an IAM policy on the resource.
C. Define an Amazon Cognito identity pool, then install the connector on the Active Directory server. Use the Amazon Cognito SDK on the application instance to authenticate the employees using their Active Directory user names and passwords.
D. Create an AWS Lambda custom authorizer as the authenticator for a reverse proxy on Amazon EC2. Ensure the security group on Amazon EC2 only allows access from the Lambda function.