When using the grade reporting feature of IMS-LTI on a non-Apache server environment, there is an issue with the use of the getallheaders() function. When attmepting to use outcome functionality with the test tool provider located at http://www.imsglobal.org/developers/LTI/test/v1p1/tool.php
an error occurs in mod/lti/service.php.
According to http://us2.php.net/manual/en/function.getallheaders.php the getallheaders function, which service.php uses, is only supported on Apache.
A workaround was defining the function if it doesn't already exist.

Steps to reproduce:

1. Install Moodle on IIS (though any non-Apache server would also likely cause this)
2. Create a new external tool activity linking to http://www.imsglobal.org/developers/LTI/test/v1p1/tool.php
3. Save and display the activity
4. Navigate to the LIS/LTI Outcome Service
5. Attempt any of the functions - service.php will error out (or no result is returned)

Potential Solution/Workaround:
Added the following to servicelib.php (solution found in comments on php documentation):

if (!function_exists('getallheaders')) 

{

    function getallheaders() 

    {

       foreach ($_SERVER as $name => $value) 

       {

           if (substr($name, 0, 5) == 'HTTP_') 

           {

               $headers[str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5)))))] = $value;

           }

       }

       return $headers;

    }

}