都2016年了，從browser上傳個圖片到S3還這麼折騰...真想罵聲暗
折騰原因：
- s3 bucket: cors
- s3 credentials
- upload to s3 from server
- upload to s3 from browser
- cognito/IAM
- ajax: signature from backend
- aws-sdk
前端
resize原圖或縮圖都要利用canvas產生縮圖，image再轉成blob (類似檔案的物件)，而後才能上傳
aws
https://github.com/aws/aws-sdk-js
以下必讀:
https://github.com/minio/minio-js
http://blog.tcs.de/post-file-to-s3-using-node/
https://blog.fineuploader.com/2013/08/16/fine-uploader-s3-upload-directly-to-amazon-s3-from-your-browser/#what-is-this
https://github.com/SwingDev/s3-browser-direct-upload
cognito/IAM
image resize:
https://github.com/rossturner/HTML5-ImageUploader
http://stackoverflow.com/questions/23945494/use-html5-to-resize-an-image-before-upload
https://hacks.mozilla.org/2011/01/how-to-develop-a-html5-image-uploader/
https://github.com/nodeca/pica
canvas to blob
http://stackoverflow.com/questions/4998908/convert-data-uri-to-file-then-append-to-formdata
http://stackoverflow.com/questions/13990673/upload-canvas-data-to-s3
https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob
http://stackoverflow.com/questions/19032406/convert-html5-canvas-into-file-to-be-uploaded
aws s3 debug tool
http://s3.amazonaws.com/doc/s3-example-code/post/post_sample.html
