AWS S3 Generating Signed Urls ''AccessDenied''

Highest upvoted answer here technically works but isn't practical since it's opening up the bucket to be public.

I had the same problem and it was due to the role that was used to generate the signed url. The role I was using had this:

- Effect: Allow
  Action: 
    - "s3:ListObjects"
    - "s3:GetObject"
    - "s3:GetObjectVersion"
    - "s3:PutObject"
  Resource:
    - "arn:aws:s3:::(bucket-name-here)"

But the bucket name alone wasn't enough, I had to add a wildcard on the end to designate access to whole bucket:

- Effect: Allow
  Action: 
    - "s3:ListObjects"
    - "s3:GetObject"
    - "s3:GetObjectVersion"
    - "s3:PutObject"
  Resource:
    - "arn:aws:s3:::(bucket-name-here)/*"

Your code is correct, double check the following things:

1. Your bucket access policy.

2. Your bucket permission via your API key.

3. Your API key and secret.

4. Your bucket name and key.

For bucket policy you can use the following:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "PublicReadGetObject",
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::bucket/*"
        }
    ]
}

Change bucket with your bucket name.

For users and access key permission (#2), you should follow these steps:

1-Goto AWS Identity and Access Management (IAM) and click on Policies link and click on "Create policy" button.

2-Select the JSON tab.

3-Enter the following statement, make sure change the bucket name and click on "review policy" button.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": "arn:aws:s3:::YOURBUCKETNAME"
        }
    ]
}

4-Enter a name for your policy and click on "Create policy" button.

5-Click on Users link, and find your current username (You already have the access key and secret for that)

6-Click on "add permission" button.

7-Add the policy we created in the previous step and save.

Finally, make sure your bucket not accessible from Public, add the correct content type to your file and set signatureVersion: 'v4'

The final code should be like this, thanks @Vaisakh PS:

const s3bucket = new AWS.S3({
    signatureVersion: 'v4',
    accessKeyId: 'my-access-key-id',
    secretAccessKey: 'my-secret-access-key',
    Bucket: 'my-bucket-name',
})
const uploadParams = {
    Body: file.data,
    Bucket: 'my-bucket-name',
    ContentType: file.mimetype,
    Key: `files/${file.name}`,
}
s3bucket.upload(uploadParams, function (err, data) {
    // ...
})
const url = s3bucket.getSignedUrl('getObject', {
    Bucket: 'my-bucket-name',
    Key: 'file-key',
    Expires: 300,
})