presigned URLs require redirect, breaking CORS

I am trying to implement a direct upload feature for a website. On the backend I generate a presigned URL so I can do the upload from the browser:

bucket = self.request.registry.settings['s3.media.bucket']
client = boto3.client('s3')
url = client.generate_presigned_url('put_object',
    Params={
        'Bucket': bucket,
        'Key': '%s/%s' % (data['category'], data['key']),
        'ACL': 'public-read',
        'ContentType': data['content_type'],
    },
    ExpiresIn=300,
    HttpMethod='PUT')

The resulting URL follows the standard naming pattern of https://<bucket>.s3.amazonaws.com/<path>. When I try to do the file upload from a browser the browser will first issue a CORS pre-flight OPTIONS request. This results in a 307 temporary redirect from AWS to https://<bucket>.*<region>*.amazonwas.com/<path>. Since redirects for CORS requests are not allowed the browser immediately aborts the request.

Is there a way to generate a URL that will not result in a redirect using boto3?

[DavyCode]

I am using AWS sdk for uploads, after spending some time searching online i stumbled upon this thread. thanks to @lsimoneau 45581857 its turns out the exact same thing was happening. I simply pointed my request Url to the region on my bucket by attaching the region property and it worked.

const s3 = new AWS.S3({ accessKeyId: config.awsAccessKeyID, secretAccessKey: config.awsSecretAccessKey, region: ‘eu-west-2’ // add region here });

[JordonPhillips]

@Chronial In that case, you should either sign the request with sigv4 or remove that function from event handler. I’ll include this use case in #425 since it’s a bit of a gotcha. For now, here’s how to use sigv4:

import boto3
from botocore.client import Config

s3 = boto3.client('s3', 'us-west-2', config=Config(signature_version='s3v4'))
s3.generate_presigned_url('list_buckets')
u'https://s3-us-west-2.amazonaws.com/?~~etc~~~'