Lack of JWT issuer and signer validation

Summary

The Amazon.ApplicationLoadBalancer.Identity.AspNetCore repo https://github.com/awslabs/aws-alb-identity-aspnetcore#validatetokensignature contains Middleware that can be used in conjunction with the Application Load Balancer (ALB) OpenId Connect integration and can be used in any ASP.NET https://dotnet.microsoft.com/apps/aspnet Core deployment scenario, including Fargate, EKS, ECS, EC2, and Lambda. In the JWT handling code, it performs signature validation but fails to validate the JWT issuer and signer identity. The signer omission, if combined with a scenario where the infrastructure owner allows internet traffic to the ALB targets (not a recommended configuration), can allow for JWT signing by an untrusted entity and an actor may be able to mimic valid OIDC-federated sessions to the ALB targets. The repository/package has been deprecated, is end of life, and is no longer supported. As a security best practice, ensure that your ELB targets (e.g. EC2 Instances, Fargate Tasks etc.) do not have public IP addresses. Ensure any forked or derivative code validate that the signer attribute in the JWT match the ARN of the Application Load Balancer that the service is configured to use.