Uploading to S3 without a server in Rails

proof-of-concept.html.erb

<% post = Aws::S3::Bucket.new(ENV.fetch('AWS_S3_BUCKET')).presigned_post(key: 'uploads/${filename}', acl: 'public-read') %>

<%= form_tag(post.url, id: 'uploader', multipart: true, authenticity_token: false, enforce_utf8: false) do %>
  <% post.fields.each do |name, value| %>
    <%= text_field_tag name, value %>
  <% end %>

  <% # Must be last field %>
  <%= file_field_tag :file %>

  <input type="submit" value="Upload">
<% end %>