"Your API key is not valid on this domain" when calling Disqus from WP7 - silverlight

Question

I'm trying to access the REST Disqus API using the following url:
http://disqus.com/api/3.0/threads/listPosts.json
?api_key=myKey
&forum=myForum
&thread:ident=myIdent
When I go to the url in Chrome, it works fine. When I try to download it in WebClient, I have difficulty:
WebClient data = new WebClient();
Uri queryUri = new Uri(DisqusQuery + ident, UriKind.Absolute);
data.DownloadStringCompleted += new DownloadStringCompletedEventHandler(onDownloadCompleted);
data.DownloadStringAsync(queryUri);
The DownloadStringCompletedEventArgs contain the following error:
{"The remote server returned an error: NotFound."}
at System.Net.Browser.ClientHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult)
at System.Net.Browser.ClientHttpWebRequest.<>c__DisplayClass2.<EndGetResponse>b__1(Object sendState)
at System.Net.Browser.AsyncHelper.<>c__DisplayClass4.<BeginOnUI>b__1(Object sendState)
at System.Reflection.RuntimeMethodInfo.InternalInvoke(RuntimeMethoThe thread '<No Name>' (0xfc10086) has exited with code 0 (0x0).
What could I be doing wrong?
Update: Looking in Fiddler shows that the response is this:
HTTP/1.1 400 BAD REQUEST
Date: Sun, 28 Aug 2011 14:51:39 GMT
Server: Apache/2.2.14 (Ubuntu)
Vary: Cookie,Accept-Encoding
p3p: CP="DSP IDC CUR ADM DELi STP NAV COM UNI INT PHY DEM"
Content-Length: 68
Connection: close
Content-Type: application/json
X-Pad: avoid browser bug
{"code": 11, "response": "Your API key is not valid on this domain"}
Here is the response when the request is from Chrome Incognito (not logged in to disqus):
HTTP/1.1 200 OK
Date: Mon, 29 Aug 2011 17:00:29 GMT
Server: Apache/2.2.14 (Ubuntu)
X-Ratelimit-Remaining: 1000
Content-Encoding: gzip
Vary: Cookie,Accept-Encoding
X-Ratelimit-Limit: 1000
p3p: CP="DSP IDC CUR ADM DELi STP NAV COM UNI INT PHY DEM"
X-Ratelimit-Reset: 1314640800
Content-Length: 3120
Connection: close
Content-Type: application/json
/* expected JSON response */
Update 2: The above error is using my public key. Using the secret key results in:
HTTP/1.1 403 FORBIDDEN
Date: Sun, 28 Aug 2011 20:40:32 GMT
Server: Apache/2.2.14 (Ubuntu)
Vary: Cookie,Accept-Encoding
p3p: CP="DSP IDC CUR ADM DELi STP NAV COM UNI INT PHY DEM"
Connection: close
Transfer-Encoding: chunked
Content-Type: application/json
2a
{"code": 5, "response": "Invalid API key"}
0

Answer 1

FIX:
Add something similar to the following line to your HttpRequest:
client.Headers[HttpRequestHeader.Referer] = "http://mywebsite.com";
Longer Description:
The problem has to do with the way Windows Phone is setting the HTTP Referer header.
When running the successful request from the browser address bar, Fiddler showed me this:
GET /api/3.0/forums/listPosts.json?forum=disqus&api_key=jRml... HTTP/1.1
Accept: */*
Accept-Language: en-US
Accept-Encoding: gzip, deflate, peerdist
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E; Zune 4.7; InfoPath.3; MS-RTC LM 8)
Connection: Keep-Alive
Host: disqus.com
Cookie: disqus_unique=...
X-P2P-PeerDist: Version=1.0
When I examined the request sent by Silverlight in Fiddler, I saw the following:
GET /api/3.0/forums/listPosts.json?forum=disqus&api_key=jRml... HTTP/1.1
Accept: */*
Referer: file:///Applications/Install/9036AAF3-F213-4CFB-B57E-576A05E1896D/Install/
Accept-Encoding: identity
User-Agent: NativeHost
Host: disqus.com
Connection: Keep-Alive
By removing the Referer header and resubmitting via Fiddler, the query worked as I expected! So... all you need to do is manually set the HTTP Referer header to something you control (rather than letting Silverlight do it for you) and you should be good to go.
Oh - and also make sure you're using your public key, not the secret key.
/ck

Answer 2

Looks like the browser is getting additional info like username or something: X-User: anon:182210122933. This is missing when WebClient gets its response back. I guess this has something todo with the fact that you are logged in in the browser or that you have a typo in your api key.
Another interesting pointroject for you would be a library like http://disqussharp.codeplex.com/ which handles authentication most of the time.
Good luck!