Generate presigned url for S3 Object Lambda

Question

Recently S3 Object Lambda got released, which I think is really cool. I have a working setup where I can use retrieve an object via the get_object BOTO3 method with the S3 Object Lambda. Also generating a presigned url directly on the bucket works. But when I try to generate one for the S3 Object Lambda as follows:
url = s3.generate_presigned_url("get_object", Params={
"Bucket": "arn:aws:s3-object-lambda:eu-west-1:account-id:accesspoint/my-object-lambda",
"Key": "filename.txt",
})
I get the error:

<?xml version="1.0" encoding="UTF-8"?><Error xmlns=""><Code>MissingAuthenticationToken</Code><Message>Missing authentication token.</Message><RequestId>REDACTED</RequestId><HostId>{host-id}</HostId></Error>

Is this not supposed to work (yet)?

Edited by: Paulvdb on Mar 31, 2021 11:17 AM

Accepted Answer

Hi Paulvdb,  
  
Glad to hear you're enjoying S3 Object Lambda.  I believe Boto3 defaults to using Signature Version 2 when presigning requests.  Can you try setting the signature version to SigV4 when creating the S3 client to see if that helps?  
  
Something like:  
  
`s3 = boto3.client('s3', config=Config(signature_version='s3v4'))`

Answer

I can confirm that this is the case. Interestingly, if you generate a presigned URL from the CLI (V2), **it will automatically default to using Sigv4**. The AWS documentation on this seems to be out of date and does not include the updated signature version needed: https://docs.aws.amazon.com/AmazonS3/latest/userguide/ShareObjectPreSignedURL.html.

What is up to date is this guide here explaining in more detail how to generate the presigned URLs with the updated signature version: https://howtocloud.io/generate-s3-presigned-urls-with-boto3/.

Kudos to the first user for including the exact same code snippet that I gave to another user who was debugging.

Answer

I was able to create presigned url using Lambda with boto3, but was no able to download the file using generated URL,
got **Access Denied** error, fix was to add lambda IAM permission : `"s3:GetObject"`

Generate presigned url for S3 Object Lambda

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