Cool, gimme a field to add a custom header (e.g. "Authorization" is pretty common) and I'll use it!
curl http://example.com -H 'Authentication: root' -H 'Password: p4ssw0rd'Curl provides a shortcut for this as --user; e.g. curl --user name:pass http://example.com
Try it yourself with -vvv to see all the headers from both ends. Ref: http://curl.haxx.se/docs/httpscripting.html#Basic_Authentica...
http basic auth protocol: http://en.m.wikipedia.org/wiki/Basic_access_authentication