Did they really have an output value of thier secret key and thier access key?

I know outputting the secret key isn't ideal. Is there another way to retrieve it after it's been generated?

You shouldn’t need the access keys at all to publish to the bucket.

How are you trying to automate publishing?

If more than one developer can publish to the bucket, you shouldn’t be sharing access keys. Each developer should have thier own user name and access keys.

Really I would automate the push to S3. There are two ways. Either have a custom lambda function that gets called as a stage in code pipeline or create a code build project that runs AWS CLI commands to push to S3 after a commit.