AWS S3 incorrect bucket object

I'm trying to upload in image to s3 using the aws-sdk. I'm able to retrieve my bucket

s3 = Aws::S3::Client.new
resp = s3.list_buckets
bucket = resp.buckets.select {|x| x.name == "mybucket"}[0]

>> bucket
>> #<struct Aws::S3::Types::Bucket name="mybucket", creation_date=2015-09-05 19:23:49 UTC>

I now have my bucket. Looking at the aws documentation and heroku's documentation I should be able to call bucket.presigned_post, however I get NoMethodError: undefined method 'presigned_post' for #<Aws::S3::Types::Bucket:0x007ff583bece10>

What am I missing here? Do I not have the correct s3 bucket object?