Calling SharePoint 2013 REST API with FBA Turned On -

i have following code works fine forms based authentication turned off, moment turn on stops working:

        string baseurl = siteurl + "/_api/";         string uristring = "web/lists/getbytitle('" + listname + "')/fields/getbyinternalnameortitle('" + displayname + "')";          networkcredential cred = credentialcache.defaultnetworkcredentials;         system.net.http.httpclient client = new system.net.http.httpclient(new httpclienthandler()         {             credentials = cred         });          client.baseaddress = new uri(baseurl);         client.defaultrequestheaders.add("accept", "application/json;odata=verbose");          servicepointmanager.servercertificatevalidationcallback = delegate(object s, x509certificate certificate, x509chain chain,                 sslpolicyerrors sslpolicyerrors)         {             return true;         };          httpresponsemessage resp = client.getasync(uristring).result;         string respstring = resp.content.readasstringasync().result; 

the response follows:

{statuscode: 403, reasonphrase: 'forbidden', version: 1.1, content: system.net.http.streamcontent, headers: { transfer-encoding: chunked x-sharepointhealthscore: 0  x-forms_based_auth_required:...) 

i have tried several things, including specifying farm account windows authentication credentials under on httpclient credentials object, have tried use authenticationheadervalue:

 client.defaultrequestheaders.authorization = new authenticationheadervalue("basic", _formatbasicauth("domain", "username", "password")); 

any highly appreciated.

for experiencing issue resolved going site permissions , setting anonymous access entire website.