How do you build URLs pointing to objects in an S3 bucket?

You only need to build expiring urls if you want to restrict access.

Here's some code to generate the signed url which expires in 3 mins.

using (var s3Client = AWSClientFactory.CreateAmazonS3Client("MyAccessKey", "MySecretKey"))
{
    GetPreSignedUrlRequest request = new GetPreSignedUrlRequest()
        .WithBucketName("MyBucketName")
        .WithKey("MyFileKey")
        .WithProtocol(Protocol.HTTP)
        .WithExpires(DateTime.Now.AddMinutes(3));

    string url = s3Client.GetPreSignedURL(request);
}