The error "Certificate Signed By Unknown Authority" may indicate your Docker container lacks ca-certificates, which are used to check against and authenticate SSL connections. Without this package, some features of CircleCI will be unable to function, such as downloading workspaces.
Error when attempting to use Workspaces:
Error downloading workspace layer for job xxxxx: RequestError: send request failed caused by: Get https://xxxxxxxx.amazonaws.com/xxxxxxxxxxxxxxxxxx: x509: certificate signed by unknown authority
Install the ca-certificates package for your Linux distribution.
Install for Alpine:
apk add ca-certificates