I figured it out.  Our i-doit instance is set to require authentication from JSON-RPC calls, which are not included in the JS files in the module.  I unchecked this option and it works.  As this is a test environment this is fine for now, but I may need to hard-code authentication at a later date when we move into production.

Dear all,

I'm hoping someone can help me here.  I'm using the ReferenceIdoitObjects module for OTRS and appear to have successfully installed it, except that when I click on the 'Reference i-doit objects' button in OTRS, I just get the 'Loading…' message.  I have followed the installation instructions.

I turned on Fiddler to try and work out exactly what the issue is and I got the following response when the module tried to call over to the i-doit server via the API proxy I set up:
Headers:

Request URL: https://{my.idoit.fqdn}/index.php?api=jsonrpc
Request Method: OPTIONS
Status Code: 200
Query Url
api: jsonrpc
Request Headers
Access-Control-Request-Method: POST
Origin: http://{my.otrs.fqdn}
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36
Access-Control-Request-Headers: accept, content-type
Accept: */*
Referer: http://{my.otrs.fqdn}/otrs/index.pl?Action=AgentReferenceIDoitObjects;TicketID=3
Accept-Encoding: gzip, deflate, sdch, br
Accept-Language: en-US,en;q=0.8
Response Headers
Date: Wed, 06 Jul 2016 16:44:07 GMT
Server: Apache/2.4.7 (Ubuntu)
X-Powered-By: PHP/5.5.9-1ubuntu4.11
Set-Cookie: PHPSESSID=rqnelm3a6vl0v1kheop31binb7; path=/
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-Length: 257
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: application/json 

Response:

{"jsonrpc":"2.0","error":{"code":-32600,"message":"Invalid request","data":{"error":"This is not a JSON-RPC. The content-type should be application\/json, request method should be \"post\" and the http body should be a valid json-rpc 2.0 package."}},"id":0}

Is there something I've misconfigured?  I believe I followed the README.md file closely, please let me know if any additional information is needed.