The -a is only meant for basic auth, which is what the core interface would use (pops up asking for user/pass). I do see that your -u is a login page, are you attempting to have it full out a page and login?
[root@suse11 libexec]# ./check_http -H 192.168.3.42 -u "/nagios/" -a "nagiosadmin:my_password"
HTTP OK: HTTP/1.1 200 OK - 1094 bytes in 0.001 second response time |time=0.000913s;;;0.000000 size=1094B;;;0
The page that this is trying to get a reply from is the diagnostic page of a larger app.
When that url is hit it asks for a UN and password to continue
Hang on ... One of our web guys just told me that it is not the un/pw that is failing it is the user agent - ie User-Agent: check_http/v2.0.3 (nagios-plugins 2.0.3)
the url that I am trying to hit is as I say a diagnostic page that is part of an application
when the url is hit it returns a standard "authentication required" dialog
When the UN/PW is authenticated a XML is returned that has "operation successful" in the first line
We have about 15 different servers that we run this against with SiteScope . I am wanting to move it to Nagios