A developer has an application that pushes files from an on-premises local server to an Amazon S3 bucket.
The application uses an AWS access key and a secret key that are stored on the server for authentication. The application calls AWS Security Token Service (AWS STS) to assume a role with access to perform the S3 PUT operation to upload the file.
The developer is migrating the server to an Amazon EC2 instance. The EC2 instance is configured with an IAM instance profile in the same AWS account that owns the S3 bucket.
What is the MOST secure solution for the developer to use to migrate the automation code?

A. Remove the code that calls the STS AssumeRole operation. Use the same access key and secret key from the server to access the S3 bucket.
B. Remove the access key and the secret key. Use the STS AssumeRole operation to add permissions to access the S3 bucket.
C. Remove the access key, the secret key, and the code that calls the STS AssumeRole operation. Use an IAM instance profile role that grants access to the S3 bucket.
D. Remove the access key, the secret key, and the code that calls the STS AssumeRole operation. Create a new access key and secret key. Use the new keys to access the S3 bucket.