Plugins: Add 'http_auth_pair' as 'http' command argument.

Fixes #6396

doc/6-configuring-icinga-2.md

@@ -1858,6 +1858,7 @@ http_vhost         | **Optional.** The virtual host that should be sent in the "
 http_uri           | **Optional.** The request URI.
 http_port          | **Optional.** The TCP port. Defaults to 80 when not using SSL, 443 otherwise.
 http_ssl           | **Optional.** Whether to use SSL. Defaults to false.
+http_auth_pair	   | **Optional.** Add 'username:password' authorization pair.
 http_warn_time     | **Optional.** The warning threshold.
 http_critical_time | **Optional.** The critical threshold.
 

itl/command-plugins.conf

@@ -121,6 +121,10 @@ object CheckCommand "http" {
 		"-S" = {
 			set_if = "$http_ssl$"
 		}
+		"-a" = {
+			value = "$http_auth_pair$"
+			description = "Username:password on sites with basic authentication"
+		}
 		"-w" = "$http_warn_time$"
 		"-c" = "$http_critical_time$"
 	}