Option Bis the correct solution because:

AWS Security Token Service (STS)allows the web application to request temporary security credentials that grant access to AWS resources. These temporary credentials are secure and short-lived, reducing the risk of misuse.

Using STS and IAM roles ensures scalability by enabling the application to dynamically assume roles with the required permissions for each AWS service.

Option A:Assigning IAM roles directly to instances is less flexible and would grant the same permissions to all applications on the instance, which is not ideal for a multi-service web application.Option C:AWS IAM Identity Center is used for managing single sign-on (SSO) for workforce users and is not designed for granting programmatic access to web applications.Option D:Storing long-term access keys, even in AWS Systems Manager Parameter Store, is less secure and does not scale well compared to temporary credentials from STS.

AWS Documentation References:

AWS Security Token Service (STS)

IAM Roles for Temporary Credentials