title: ActiveStorage to upload large base64 encoded string?
body: <p>If I have an image that was edited/generated using JavaScript on the client (for example, a cropped photo or the result of a canvas drawing), is there a way to upload it using ActiveStorage?</p>
  
  <p>It would typically be a large string containing <code>"&lt;img src='data:image/jpeg;base64,...=='&gt;"</code> that is stored in a JavaScript variable, not a file.</p>