Plugins that request Awasu download a file on their behalf (via the DownloadUrl parameter) can now also specify authentication details (via DownloadUrl_UserName and DownloadUrl_Password).
As best I can tell, Awasu (both "normally" and when downloading a DownloadUrl) identifies itself with User-Agent Awasu/2.0.4AE.
Could Awasu also support a DownloadUrl_Agent (or somesuch) string? Some sites refuse to respond unless they are apparently dealing with one of several "official" browsers, so this could allow a transfer to work that would otherwise fail.
While you're at it , could you also provide a new channel parameter in a plug-in's .ini file: DownloadUrlEncoding? This would return any 'charset' value specified in the page's Content-Type.