Generate a S3 pre-signed url using cloudflare worker.

cloudflare-s3.ts

import * as AWS from 'aws-sdk';
# Your S3 compatible API secrets
declare var AWS_ACCESS_KEY: string;
declare var AWS_SECRET_ACCESS_KEY: string;
# Your endpoint and bucket name.
const S3_ENDPOINT = 'example.myapp.xyz';
const S3_BUCKET = 'mybucket';
const s3 = new AWS.S3({
  credentials: new AWS.Credentials(AWS_ACCESS_KEY, AWS_SECRET_ACCESS_KEY),
  endpoint: new AWS.Endpoint(S3_ENDPOINT),
  signatureVersion: 'v4',
  s3ForcePathStyle: true
});
const TTL_SECONDS = 5 * 60;

addEventListener('fetch', (event) => {
  event.respondWith(handleRequest(event))
})

class ApiResponse extends Response {
  constructor(body?: BodyInit | null, init?: ResponseInit) {
    super(body, init)
    this.headers.set("Access-Control-Allow-Origin", "*");
  }
}

export async function handleRequest(event: FetchEvent): Promise<Response> {
  let response;
  let file = event.request.url.split('/download/token/')[1];

  if (!file) {
    response = {
      status: 400,
      error: 'Bad url, missing resource'
    };
  } else {
    const url = s3.getSignedUrl('getObject', {
      Bucket: S3_BUCKET,
      Key: file,
      Expires: TTL_SECONDS
    });

    response = {
      url: url,
      resource: file
    };
  }
  const ret = new ApiResponse(JSON.stringify(response, null, 4), {
    status: response.status
  });
  return ret;
}