http post to login in c# -

i'm noob in c# programming.

i want implement http post login on web server. correct implemetation (test advanced rest) http post http://localhost:8080/pentaho/j_spring_security_check "j_username=admin&j_password=password" payload , application encoded content type . advanced rest, server responses 302 , redirects home (and right way).

i tried implement same thing in c# code (copied google) server responsens 500 ....

here code:

public partial class webform1 : system.web.ui.page {

    private static readonly httpclient client = new httpclient();       protected void page_load(object sender, eventargs e)     {      }      private void dorequest()     {         // create request using url can receive post.          webrequest request = webrequest.create("http://localhost:8080/pentaho/j_spring_security_check");         // set method property of request post.         request.method = "post";         // create post data , convert byte array.         string postdata = "j_username=admin&j_password=password";         byte[] bytearray = encoding.utf8.getbytes(postdata);         // set contenttype property of webrequest.         request.contenttype = "application/x-www-form-urlencoded";         // set contentlength property of webrequest.         request.contentlength = bytearray.length;         // request stream.         stream datastream = request.getrequeststream();         // write data request stream.         datastream.write(bytearray, 0, bytearray.length);         // close stream object.         datastream.close();                      // response.         webresponse response = request.getresponse();         // display status.         console.writeline(((httpwebresponse)response).statusdescription);         // stream containing content returned server.         datastream = response.getresponsestream();         // open stream using streamreader easy access.         streamreader reader = new streamreader(datastream);         // read content.         string responsefromserver = reader.readtoend();         // display content.         console.writeline(responsefromserver);         // clean streams.         reader.close();         datastream.close();         response.close();     }     protected void button1_click(object sender, eventargs e)     {         dorequest();     } } 

can me? many in advance

edit: here stack trace

system.dll!system.net.httpwebrequest.getresponse()  sconosciuto 

edoc_giocattolo2.dll!edoc_giocattolo2.webform1.dorequest() riga 45 c# edoc_giocattolo2.dll!edoc_giocattolo2.webform1.button1_click(object sender, system.eventargs e) riga 63 c# system.web.dll!system.web.ui.webcontrols.button.onclick(system.eventargs e) sconosciuto system.web.dll!system.web.ui.webcontrols.button.raisepostbackevent(string eventargument) sconosciuto system.web.dll!system.web.ui.webcontrols.button.system.web.ui.ipostbackeventhandler.raisepostbackevent(string eventargument) sconosciuto system.web.dll!system.web.ui.page.raisepostbackevent(system.web.ui.ipostbackeventhandler sourcecontrol, string eventargument) sconosciuto system.web.dll!system.web.ui.page.raisepostbackevent(system.collections.specialized.namevaluecollection postdata) sconosciuto system.web.dll!system.web.ui.page.processrequestmain(bool includestagesbeforeasyncpoint, bool includestagesafterasyncpoint) sconosciuto system.web.dll!system.web.ui.page.processrequest(bool includestagesbeforeasyncpoint, bool includestagesafterasyncpoint) sconosciuto system.web.dll!system.web.ui.page.processrequest() sconosciuto system.web.dll!system.web.ui.page.processrequestwithnoassert(system.web.httpcontext context) sconosciuto system.web.dll!system.web.ui.page.processrequest(system.web.httpcontext context) sconosciuto app_web_kky3vf3s.dll!asp.webform1_aspx.processrequest(system.web.httpcontext context) c# system.web.dll!system.web.httpapplication.callhandlerexecutionstep.system.web.httpapplication.iexecutionstep.execute() sconosciuto system.web.dll!system.web.httpapplication.executestep(system.web.httpapplication.iexecutionstep step, ref bool completedsynchronously) sconosciuto system.web.dll!system.web.httpapplication.pipelinestepmanager.resumesteps(system.exception error) sconosciuto system.web.dll!system.web.httpapplication.beginprocessrequestnotification(system.web.httpcontext context, system.asynccallback cb) sconosciuto system.web.dll!system.web.httpruntime.processrequestnotificationprivate(system.web.hosting.iis7workerrequest wr, system.web.httpcontext context) sconosciuto system.web.dll!system.web.hosting.pipelineruntime.processrequestnotificationhelper(system.intptr rootedobjectspointer, system.intptr nativerequestcontext, system.intptr moduledata, int flags) sconosciuto system.web.dll!system.web.hosting.pipelineruntime.processrequestnotification(system.intptr rootedobjectspointer, system.intptr nativerequestcontext, system.intptr moduledata, int flags) sconosciuto [transizione da nativo gestito]
[transizione da gestito nativo]
system.web.dll!system.web.hosting.pipelineruntime.processrequestnotificationhelper(system.intptr rootedobjectspointer, system.intptr nativerequestcontext, system.intptr moduledata, int flags) sconosciuto system.web.dll!system.web.hosting.pipelineruntime.processrequestnotification(system.intptr rootedobjectspointer, system.intptr nativerequestcontext, system.intptr moduledata, int flags) sconosciuto [transizione appdomain]

edit: added cast (httpwebrequest) , have not 500 internal error. can't see post request in firebug , i'm not logged in server :(

so, don't have error. printed html response (as text in console) , looks same of source page html obtained manual login. if redirect server, i'm not logged in!

any suggestion?