Returns a pre-signed GET URL to download the S3 object in the specified bucket under the specified key.
Pre-signed URLs are useful for enabling direct third-party browser access to your private Amazon S3 data, without proxying the request, or exposing your AWS secret access key. The pre-signed request is encoded as a URL that any end-user's browser can retrieve.
Pre-signed requests are limited by the specified expiration time. Once the expiration time passes, the pre-signed URL will stop working.
@param bucketName The name of the bucket containing the desired object.
@param key The key in the specified bucket under which the desired object is stored.
@param expiration The time at which the returned pre-signed URL will expire.
@return A pre-signed URL which expires at the specified time, and can beused to allow anyone to download the specified object from S3, without exposing the owner's AWS secret access key.
@throws AmazonClientException If there were any problems pre-signing the request for the specified S3 object.