Getting 403 (Forbidden) when uploading to S3 with a signed URL

Your request needs to match the signature, exactly. One apparent problem is that you are not actually including the canned ACL in the request, even though you included it in the signature. Change to this:

var options = { headers: { 'Content-Type': fileType, 'x-amz-acl': 'public-read' } };

Receiving a 403 Forbidden error for a pre-signed s3 put upload can also happen for a couple of reasons that are not immediately obvious:

1. It can happen if you generate a pre-signed put url using a wildcard content type such as image/*, as wildcards are not supported.

2. It can happen if you generate a pre-signed put url with no content type specified, but then pass in a content type header when uploading from the browser. If you don't specify a content type when generating the url, you have to omit the content type when uploading. Be conscious that if you are using an upload tool like Uppy, it may attach a content type header automatically even when you don't specify one. In that case, you'd have to manually set the content type header to be empty.

In any case, if you want to support uploading any file type, it's probably best to pass the file's content type to your api endpoint, and use that content type when generating your pre-signed url that you return to your client.

For example, generating a pre-signed url from your api:

const AWS = require('aws-sdk')
const uuid = require('uuid/v4')

async function getSignedUrl(contentType) {
    const s3 = new AWS.S3({
        accessKeyId: process.env.AWS_KEY,
        secretAccessKey: process.env.AWS_SECRET_KEY
    })
    const signedUrl = await s3.getSignedUrlPromise('putObject', {
        Bucket: 'mybucket',
        Key: `uploads/${uuid()}`,
        ContentType: contentType
    })

    return signedUrl
}

And then sending an upload request from the browser:

import Uppy from '@uppy/core'
import AwsS3 from '@uppy/aws-s3'

this.uppy = Uppy({
    restrictions: {
        allowedFileTypes: ['image/*'],
        maxFileSize: 5242880, // 5 Megabytes
        maxNumberOfFiles: 5
    }
}).use(AwsS3, {
    getUploadParameters(file) {
        async function _getUploadParameters() {
            let signedUrl = await getSignedUrl(file.type)
            return {
                method: 'PUT',
                url: signedUrl
            }
        }

        return _getUploadParameters()
    }
})

For further reference also see these two stack overflow posts: how-to-generate-aws-s3-pre-signed-url-request-without-knowing-content-type and S3.getSignedUrl to accept multiple content-type