If this is an answered question, please excuse me and point me in the right direction.

I'm working on a web-based system that leverages FME server to run serveral tasks and provides the result to the user.

By programatically building parameters and calling the FME Server data download endpoint at

$"{repository.Url}/fmedatadownload/{repository.RepositoryName}/{analysis.WorkspaceId}";

and setting the parameter opt_servicemode to sync I get a response on the form:

{  
   "serviceResponse":{  
      "jobID":10261,
      "statusInfo":{  
         "mode":"sync",
         "status":"success"
      },
      "fmeTransformationResult":{  
         "fmeEngineResponse":{  
            "outputLocation":"C:\\\\ProgramData\\\\Safe Software\\\\FME Server\\\\resources\\\\system\\\\temp\\\\engineresults\\\\FME_176D3A2A_1504696983768_3368.zip",
            "resultRootDir":"/fmedatadownload/results",
            "statusNumber":"0",
            "logFileName":"job_10261.log",
            "downloadUrl":"http://server/fmedatadownload/results/FME_176D3A2A_1504696983768_3368.zip",
            "numFeaturesOutput":"49",
            "statusMessage":"Translation Successful",
            "notificationLocation":"C:\\\\ProgramData\\\\Safe Software\\\\FME Server\\\\resources\\\\system\\\\temp\\\\engineresults\\\\FME_176D3A2A_1504696983768_3368_nw"
         },
         "fmeServerResponse":{  
            "request":"\\"            Samples/austinApartments/austinApartments.fmw\\" -XML_PARAMETER <?xml version=\\"1.0\\" encoding=\\"UTF-8\\"?>\<TRANSFORMATION_REQUEST><PUBLISHED_PARAMETER name=\\"FME_SERVER_REQUEST_HEADERS\\">            {  
               \\"remote-addr\\":\\"192.168.46.110\\",
               \\"host\\":\\"192.168.4.148\\"
            }            <\\/PUBLISHED_PARAMETER><PUBLISHED_PARAMETER name=\\"FME_SERVER_REQUEST_URI\\">http://server//fmedatadownload/Samples/austinApartments.fmw<\\/PUBLISHED_PARAMETER><PUBLISHED_PARAMETER name=\\"FME_SERVER_REQUEST_PARAMETERS\\">            {  
               \\"opt_responseformat\\":\\"json\\",
               \\"opt_servicemode\\":\\"sync\\"
            }            <\\/PUBLISHED_PARAMETER><\\/TRANSFORMATION_REQUEST> --FME_SECURITY_USER \\"admin\\" --FME_SECURITY_ROLES \\"fmeadmin fmesuperuser\\" --FME_SERVER_HOST \\"localhost\\" --FME_SERVER_PORT \\"7071\\" --FME_SERVER_WEB_URL \\"http:            //192.168.4.148:80            \\" -OGCKML_1_DATASET \\"!FME_AUTO_DIR_NAME!.zip\\\\austinApartments.kml\\"",
            "jobStatus":"SUCCESS",
            "timeRequested":"Wed-06-Sep-2017 01:23:03 PM",
            "requestKeyword":"FILE_DOWNLOAD_SERVICE",
            "description":"",
            "timeStarted":"2017-09-06 01:23:03",
            "requesterHost":"192.168.4.148",
            "priority":"100",
            "result":"0:Translation Successful|NotificationLocation=C:\\\\ProgramData\\\\Safe Software\\\\FME Server\\\\resources\\\\system\\\\temp\\\\engineresults\\\\FME_176D3A2A_1504696983768_3368_nw|OutputLocation=C:\\\\ProgramData\\\\Safe Software\\\\FME Server\\\\resources\\\\system\\\\temp\\\\engineresults\\\\FME_176D3A2A_1504696983768_3368.zip|ResultRootDir=/fmedatadownload/results|NumFeaturesOutput=49|LogFileName=job_10261.log|downloadUrl=http://server/fmedatadownload/results/FME_176D3A2A_1504696983768_3368.zip",
            "requesterResultPort":"55697",
            "resultSuccess":"true",
            "serviceSuccess":"true",
            "id":"10261",
            "timeFinished":"2017-09-06 01:23:04",
            "serviceMsg":""
         }
      },
      "url":"http://server/fmedatadownload/results/FME_176D3A2A_1504696983768_3368.zip"
   }
}

Downloading the result at url works as expected.

However. As far as my understanding of FME server goes, under heavy loads things are queued up. This means that a job submitted to the DataDownload endpoint might "run" for more than 10 minutes. This would make the HTTP request time out. 

Because of this I'm thinking that opt_servicemode = async is a better solution. If I set this, the response I get is:

{     "serviceResponse":{        "jobID":10266,      "statusInfo":{           "mode":"async",         "status":"success"      }   }}

That is, almost no info. But I do get a jobID, so I'm guessing that this serves as a reference to the job. 

And, indeed, if i navigate my browser to http://server/fmeserver/#/job/10266/summary i see a "Data DownloadURL" on top of the page, as well as in the "Result Data" section at the bottom of the page. 

However, i cannot find this url in either the response to the DataDownload request, neither as a response to any of the endpoints at http://server/fmerest/v2/transformations/jobs/id/10266

So, my questions are basically:

1) How is the data download endpoint supposed to work in async mode? Am I supposed to get a link somehow?

2) Where is the data-download-link provided?

NOTE: The sync download works as expected, but this is not the problem I'm trying to solve. I am also aware that FME server can send the result by email if I specify opt_requesteremail, but this is not what I want either. 

Any answers or pointers welcome.