"When you send API requests to AWS, you sign the requests so that AWS can identify who sent them. You sign requests with your AWS access key, which consists of an access key ID and secret access key. Some requests don’t need to be signed, including anonymous requests to Amazon Simple Storage Service (Amazon S3) and some API operations in AWS Security Token Service (AWS STS) such as AssumeRoleWithWebIdentity."

​https://docs.aws.amazon.com/general/latest/gr/signing_aws_api_requests.html​