Examples of uploading to S3 using presigned URLs and presigned POST.
This repo has an accompanying blog post: S3 Uploads - Proxies vs Presigned URLs vs Presigned POSTs.
Run npm install then serverless deploy in the backend directory.
This will create an S3 bucket, two Lambda functions, and an API Gateway REST API.
Focus on post-signer.js and url-signer.js.
Open client.html in the frontend directory.
Replace the example URL with the one from your deployed backend.
Focus on presigned-post.js and presigned-url.js.