You are building a web application that will allow authenticated users to upload videos to the AWS S3 bucket across multiple domains. However, while testing the application, you found that the upload requests to S3 are being blocked. What should you do to make the upload work?

Answer options:

A.Enable public access to allow uploads from web applications.
B.Add configuration in S3 bucket CORS to allow PUT requests from web application URL.
C.Add Content-Length and Content-MD5 headers while sending upload requests to S3
D.Web application URL must be added to bucket policy to allow PutObject requests.

Answer: B
Cross-origin resource sharing (CORS) defines a way for client web applications loaded in one domain to interact with resources in a different domain. With CORS support, you can build rich client-side web applications with Amazon S3 and selectively allow cross-origin access to your Amazon S3 resources.
For more information on CORS, refer to documentation here. https://docs.aws.amazon.com/AmazonS3/latest/dev/cors.html#example-scenarios-cors
For option A, enabling public access will not enable the web application to send requests to the S3 bucket. Furthermore, AWS does not recommend enabling public access on an S3 bucket unless you are hosting static assets that all can access.
For more information on securing S3 buckets, refer to documentation here:https://aws.amazon.com/premiumsupport/knowledge-center/secure-s3-resources/
For option C, Content-Length and Content-MD5 are system metadata for objects. They are set while creating/uploading an object. However, these parameters do not enable web applications to send requests to the S3 bucket.
For option D, the AWS S3 bucket policy does not grant permissions based on the web application.
URLs.
However, you can set up a condition in the policy to restrict access only if the request is being sent from a certain URL using the “aws:Referer” context-key.
https://docs.aws.amazon.com/AmazonS3/latest/dev/example-bucket-policies.html#example- bucket-policies-use-case-4