You can on your own server - WildCard have expressed concern for abuse of an API in regards to: for reasons of websecurity and site performance, we can not handle the web notifications for unofficial servers. So we have exposed the system for custom use, if anyone wants to write a basic web service -
To handle alarm web notifcations on a custom server, you have to start your server with "-webalarm" and have a valid AlarmPostCredentials.txt in your Saved/ folder. AlarmPostCredentials.txt is a text file that contains two lines of data. The first line is a web api key and the other is the url to use.
e.g., /ShooterGame/Saved/AlarmPostCredentials.txt
01234abcedf01234abcedf https://mywebsite.com/index.php?myowncustom=thing&another=thing
Note: You don't actually have to handle a valid key on webservice side if you don't want to but you will still have to have something inside this file.
The server will make a HTTP POST with "application/x-www-form-urlencoded" data that includes key, steamid, title, and message.
e.g., key=01234abcedf01234abcedf&steamid=0000000000001234¬etitle=Example%2BTitle&message=Example+Message