Amazon AWS S3 browser-based upload using POST -

Question

I am building a web application that includes a file upload feature. My goal is to initiate upload from users directly to an S3 bucket. The strategy is to pre-sign a POST re

Answer 1

Been a few years since the last response, but I've been stuck on this for the last day or two so I'll share my experience for anyone it may help.

I had been getting the error: "403: The AWS Access Key Id you provided does not exist in our records" when trying to upload to an s3 bucket via my presigned url.

I was able to successfully generate a presigned url similarly to above, using the server-side code:

signed_url_dict = self.s3_client.generate_presigned_post(
                self.bucket_name,
                object_name,
                ExpiresIn=300

This returned a dictionary with the structure:

{
    url: "https://___",
    fields: {
        key: "___",
        AWSAccesKeyId: "___",
        x-amz-security-token: "___",
        policy: "___",
        signature: "___"
    }
}

This lead to the part where things were a little different now in 2019 with the browser-side javascript, where the required form inputs seem to have changed. Instead of setting up the form as OP did, I had to create my form as seen below:

            
            
            
            
            
            
        File:
             

            
        

My error was that I followed an example in the boto3 1.9.138 docs and left out "x-amz-security-token" on the form, which turned out to be quite necessary. A thoughtless oversight on may part, but hopefully this will help someone else.

EDIT: My results above were based on a N. Virginia Lambda Function. When I ran generate_presigned_post(...) in Ohio (the region containing my bucket), I got results similar to OP:

{
  "url": "https://__",
  "fields": {
    "key": "___",
    "x-amz-algorithm": "___",
    "x-amz-credential": "___",
    "x-amz-date": "___",
    "x-amz-security-token": "___",
    "policy": "___",
    "x-amz-signature": "___"
  }
}

Perhaps the results of the function are region specific?