What's the difference insecurity a browser and a web client?

I have 开发者_运维知识库an ASP.Net page that does some file IO work. When I request it from a web browser, namely chrome, it succeeds, but when I request it from a WebClient instance in my application it gives me a 'System.Security.SecurityException'. Are there significant differences in the two requests? What do I need to do know about code-access-security in order to get this page to work from within my Web Client?

Here is the raw fiddler requests and responses:

Browser Request:

GET http://192.168.1.89/QuickCutConsoleDataProvider/UpdateItemFiles.aspx HTTP/1.1
Host: 192.168.1.89
Proxy-Connection: keep-alive
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3

Browser Response:

HTTP/1.1 200 OK
Via: 1.1 PHOBOS
Connection: Keep-Alive
Proxy-Connection: Keep-Alive
Content-Length: 35189
Date: Tue, 14 Dec 2010 14:08:46 GMT
Content-Type: application/zip
Server: Microsoft-IIS/7.5
Cache-Control: private
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET

... Binary Content ...

Web Client Request:

POST http://192.168.1.89/QuickCutConsoleDataProvider/UpdateItemFiles.aspx?Guid=e30e1826-3d96-4769-a540-acd911cccf02 HTTP/1.1
Content-Type: multipart/form-data; boundary=---------------------8cd697dcbf75ed4
Host: 192.168.1.89
Content-Length: 303
Expect: 100-continue

-----------------------8cd697dcbf75ed4
Content-Disposition: form-data; name="file"; filename="Catalog.xml"
Content-Type: application/octet-stream

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<catalog version="1.0">
  <items />
</catalog>
-----------------------8cd697dcbf75ed4--

Web Client Response (exception):

HTTP/1.1 200 OK
Via: 1.1 PHOBOS
Connection: Keep-Alive
Proxy-Connection: Keep-Alive
Content-Length: 1244
Date: Tue, 14 Dec 2010 14:12:34 GMT
Content-Type: text/xml; charset=utf-8
Server: Microsoft-IIS/7.5
Cache-Control: private
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET

<error type="System.Security.SecurityException">
  <message>Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.</message>
  <stack-trace><![CDATA[   at System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet)
   at System.Security.CodeAccessPermission.Demand()
   at System.IO.File.GetLastWriteTimeUtc(String path)
   at Ionic.Zip.ZipEntry.Create(String nameInArchive, ZipEntrySource source, Object arg1, Object arg2)
   at Ionic.Zip.ZipEntry.CreateFromFile(String filename, String nameInArchive)
   at Ionic.Zip.ZipFile.AddFile(String fileName, String directoryPathInArchive)
   at Ionic.Zip.ZipFile.AddFile(String fileName)
   at MyApplication.UpdateItemFiles.GetUpdateContent(XDocument a_xManifest, Stream[] a_arrExtraContent) in C:\Software\MyApplication\Alpha\Web Interface\UpdateItemFiles.aspx.cs:line 282
   at MyApplication.UpdateItemFiles.Page_Load(Object sender, EventArgs e) in C:\Software\MyApplication\Alpha\Web Interface\UpdateItemFiles.aspx.cs:line 31]]></stack-trace>
  <inner-exception>null</inner-exception>
</error>

This is very much still running in windows authentication - although you believe you have changed it. I bet impersonation is also on.

Double check the authentication. Spit out some debug code to log current identity when it is doing the IO operation.

The problem had nothing to do with IIS authentication. It was the Zip library I was using, DotNetZip. CAS wasn't willing to give it File IO permissions. I finally had to proxy IO operations with file streams. The only downside is that ever file I wanted to add to the Zip archive, I had to leave a stream open until the archive was saved. They were file streams so there was very little memory used.

Someone mentioned WCF, and that would have been ideal, but the decision maker decided that that way was to expensive.