I have been working on an iPhone app that has a feature of uploading photos to TwitPic. I have it working with basic authentication.

I am trying to get it working with OAuth. I am getting authentication errors. I have studied very carefully the TwitPic documentation.

I am authorising the app by displaying a UI Web View and the it returns a PIN value. I enter the PIN value in the app and request the token.

I am able to upload status updates to Twitter but not photos.

My code is based on some example code from here:

Example iPhone app using OAuth

Here is my code:

NSString *url = @"http://api.twitpic.com/2/upload.json";
NSString *oauth_header = [oAuth oAuthHeaderForMethod:@"POST" andUrl:url andParams:nil];

NSLog(@"OAuth header : %@\n\n", oauth_header);

ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:[NSURL URLWithString:url]];
[request addRequestHeader:@"User-Agent" value:@"ASIHTTPRequest"];
request.requestMethod = @"POST";

[request addRequestHeader:@"X-Auth-Service-Provider" value:@"https://api.twitter.com/1/account/verify_credentials.json"];   

[request addRequestHeader:@"X-Verify-Credentials-Authorization" value:oauth_header];    

NSData *imageRepresentation = UIImageJPEGRepresentation(imageToUpload, 0.8);        
[request setData:imageRepresentation forKey:@"media"];
[request setPostValue:@"Some Message"  forKey:@"message"];  
[request setPostValue:TWITPIC_API_KEY  forKey:@"key"];  

[request setDelegate:self];
[request setDidFinishSelector:@selector(requestDone:)];
[request setDidFailSelector:@selector(requestFailed:)];

[request start];    

Here is the OAuth Header:

OAuth realm="http://api.twitter.com/", oauth_timestamp="1275492425", oauth_nonce="b686f20a18ba6763ac52b689b2ac0c421a9e4013", oauth_signature_method="HMAC-SHA1", oauth_consumer_key="zNbW3Xi3MuS7i9cpz6fw", oauth_version="1.0", oauth_token="147275699-jmrjpwk3B6mO2FX2BCc9Ci9CRBbBKYW1bOni2MYs", oauth_signature="d17HImz6VgygZgbcp845CD2qNnI%3D"