I don't think the translation of curl -u <AUTH_ID>:<AUTH_TOKEN> to default_headers => { AUTH_ID=>..., AUTH_TOKEN=>... } is correct. In curl, -u specifies a username/password for authentication, the equivalent in HTTP::Tiny (and therefore HTTP::Tinyish, I assume) is to include a username:password in the URL - but it supports Basic Authentication only. See the HTTP::Tiny docs for details, but if you have to support Digest Auth, you might need to switch to something like LWP.