code: def sign_s3_upload(self):
          
          AWS_ACCESS_KEY = self.config_('AWS_ACCESS_KEY_ID')
          AWS_SECRET_KEY = self.config_('AWS_SECRET_ACCESS_KEY')
          S3_BUCKET = self.config_('AWS_S3_BUCKET_NAME')
  
          object_name = request.args.get('s3_object_name')
          mime_type = request.args.get('s3_object_type')
          expires = long(time.time()+10)
          amz_headers = "x-amz-acl:public-read"
          put_request = "PUT\n\n%s\n%d\n%s\n/%s/%s" % (mime_type, expires, amz_headers, S3_BUCKET, object_name)
          signature = base64.encodestring(hmac.new(AWS_SECRET_KEY, put_request, sha1).digest())
          signature = urllib.quote(urllib.quote_plus(signature.strip()))
          url = 'https://s3.amazonaws.com/%s/%s' % (S3_BUCKET, object_name)
          return jsonify({
              'signed_request': '%s?AWSAccessKeyId=%s&Expires=%d&Signature=%s' % (url, AWS_ACCESS_KEY, expires, signature),
               'url': url
            })
docs: Allow to create Signed object to upload to S3 via JS