Which action should be taken to share the S3 bucket?
Update the bucket to be a Requester Pays bucket.
Update the bucket to enable cross-origin resource sharing (CORS).
Create a bucket policy to require users to grant bucket-owner-full-control when uploading objects.
Create an IAM policy to require users to grant bucket-owner-full-control when uploading objects.
Explanations:
Making the bucket a Requester Pays bucket means that the requester (the vendor) must pay for requests and data retrievals. This does not address the requirement for the bucket owner to access all objects, and it is not relevant to sharing the bucket.
Enabling cross-origin resource sharing (CORS) allows web applications in one domain to access resources in another domain, but it does not provide access permissions to objects in the S3 bucket for the bucket owner or the vendor. It is more relevant for web applications than for sharing bucket access.
Creating a bucket policy that requires users to grantbucket-owner-full-controlwhen uploading objects ensures that the bucket owner retains full control over the objects uploaded by the vendor. This is the correct way to ensure the bucket owner has access to all objects in the shared bucket.
Creating an IAM policy does not enforce permissions on the objects themselves. IAM policies control user permissions but do not directly affect object ownership or access rights in the S3 bucket. This approach would not guarantee that the bucket owner has access to all uploaded objects.
I calculate that the answer is:
Create a bucket policy to require users to grant bucket-owner-full-control when uploading objects.