title: Raw request made by boto3
body: <p>I want to intercept the request which is happening under the hood of the following snippet of code:</p>
  
  <pre><code>s3 = boto3.client(
          's3', 
          aws_access_key_id=ACCESS_KEY,
          aws_secret_access_key=SECRET_KEY
          )
  
  presigned_post = s3.generate_presigned_post(
          Bucket = S3_BUCKET,
          Key = file_name,
          Fields = {"acl": "public-read", "Content-Type": file_type},
          Conditions = [
              {"acl": "public-read"},
              {"Content-Type": file_type}
              ],
          ExpiresIn = 3600
          )
  </code></pre>
  
  <p>I didn't find any docs from amazon explaining how to make those requests by hand. I need to implement the behavior above in Elixir, which doesn't have an AWS SDK available.</p>
  
  <p>How can I intercept the request to create it manually elsewhere?</p>