OAuthConsumer and Twitpic

I'm trying to post images to TwitPic using OAuthConsumer. I keep receiving a 401 "Could not authenticate you (header rejected by twitter)." error.

I am also making use of the Twitter+OAuth library to handle the login and posting regular tweets, and then saving the token and token secret for using with TwitPic.

This is the code I am using the construct the request:

NSURL *twitpicUrl = [NSURL URLWithString:@"http://api.twitpic.com/2/upload.json"];
NSString* realm = @"http://api.twitter.com/";
OAToken* oaToken = [[OAToken alloc] initWithKey:savedToken secret:savedTokenSecret];
OAConsumer* oaConsumer = [[OAConsumer alloc] initWithKey:kOAuthConsumerKey secret:kOAuthConsumerSecret];

OAMutableURLRequest *request = [[[OAMutableURLRequest alloc] initWithURL:twitpicUrl consumer:oaConsumer
                                    token:oaToken realm:realm signatureProvider:nil] autorelease];
[request prepare];
[request setHTTPMethod:@"POST"];
[request setValue:@"https://api.twitter.com/1/account/verify_credentials.json" forHTTPHeaderField:@"X-Auth-Service-Provider"];

NSString* authorizeHeader = [request valueForHTTPHeaderField:@"Authorization"];
[request setValue:authorizeHeader forHTTPHeaderField:@"X-Verify-Credentials-Authorization"];

And if I print out my headers, this is what I get (excluding the unused Authorization header):

    "X-Auth-Service-Provider" = "https://api.twitter.com/1/account/verify_credentials.json";
    "X-Verify-Credentials-Authorization" = "OAuth realm=\"http%3A%2F%2Fapi.twitter.com%2F\", oauth_consumer_key=\"JOvwW7mtZUjRXZRInkQI7w\", oauth_token=\"293217559-pD0HL0oE6TZSkU35mPnc7kia325oPDgMfQMTVArK\", oauth_signature_method=\"HMAC-SHA1\", oauth_signature=\"ctmCK35JFwx8qs8lQj0AYB6sUr4%3D\", oauth_timestamp=\"1304580843\", oauth_nonce=\"7EBE3EB0-641A-40EA-A57C-8D071B5E647F\", oauth_version=\"1.0\"";

The error I receive is:

Error: The operation couldn’t be completed. (NSURLErrorDomain error -1012.)
{"errors":[{"code":401,"message":"Could not authenticate you (header rejected by twitter)."}]}

I have excluded some detail here, specifically appending the post data, mainly because I don't think it's relevant to the error. If you think otherwise let me know and I'll update the question.

Can anyone help?

Update: Here is the code that I am now using successfully

In header:

#define kVerifyCredentialsUrl @"https://api.twitter.com/1/account/verify_credentials.json"
#define kTwitPicUrl @"http://api.twitpic.com/2/upload.json"

Implementation:

//prepare the verify credentials header
NSURL* serviceUrl = [NSURL URLWithString:kVerifyCredentialsUrl];
NSString* realm = @"http://api.twitter.com/";
OAToken* token = [[OAToken alloc] initWithKey:tokenKey secret:tokenSecret];
OAConsumer* consumer = [[OAConsumer alloc] initWithKey:kOAuthConsumerKey secret:kOAuthConsumerSecret];
OAMutableURLRequest *request = [[OAMutableURLRequest alloc] initWithURL:serviceUrl consumer:consumer token:token realm:realm signatureProvider:nil];
[request setHTTPMethod:@"GET"];
[request prepare];
NSDictionary* headerDictionary = [request allHTTPHeaderFields];
NSString* oAuthHeader = [NSString stringWithString:[headerDictionary valueForKey:@"Authorization"]];
[request release];
request = nil;

//prepare the full request
serviceUrl = [NSURL URLWithString:kTwitPicUrl];
request = [[OAMutableURLRequest alloc] initWithURL:serviceUrl consumer:consumer token:token realm:realm signatureProvider:nil];
[request setHTTPMethod:@"POST"];
[request setValue:kVerifyCredentialsUrl forHTTPHeaderField:@"X-Auth-Service-Provider"];
[request setValue:oAuthHeader forHTTPHeaderField:@"X-Verify-Credentials-Authorization"];

//add the content and start the request
UIImage* imageToUpload = [UIImage imageNamed:@"test.png"];
NSData *data = UIImagePNGRepresentation(imageToUpload);
ASIFormDataRequest *asiRequest = [[[ASIFormDataRequest alloc] initWithURL:[NSURL URLWithString:kTwitPicUrl]] autorelease];
[asiRequest addRequestHeader:@"X-Auth-Service-Provider" value:kVerifyCredentialsUrl];
[asiRequest addRequestHeader:@"X-Verify-Credentials-Authorization" value:oAuthHeader];
[asiRequest setPostValue:@"Message here" forKey:@"message"];
[asiRequest setPostValue:kTwitPicAPIKey forKey:@"key"];
[asiRequest setData:data forKey:@"media"];
[asiRequest setDidFinishSelector:@selector(requestDone:)];
[asiRequest setDidFailSelector:@selector(requestWentWrong:)];
[asiRequest setDelegate:self];
[asiRequest startAsynchronous];

Try this :

NSURL *serviceURL = [NSURL URLWithString:@"https://api.twitter.com/1/account/verify_credentials.json"];
OAMutableURLRequest *oRequest = [[OAMutableURLRequest alloc] initWithURL:serviceURL
                                                                consumer:consumer_
                                                                   token:accessToken_
                                                                   realm:@"http://api.twitter.com/"
                                                       signatureProvider:nil];
[oRequest setHTTPMethod:@"GET"];
[oRequest prepare];
NSDictionary * headerDict = [oRequest allHTTPHeaderFields];
NSString * oauthHeader = [NSString stringWithString:[headerDict valueForKey:@"Authorization"]];
[oRequest release];

//  Prepare the POST request
oRequest = nil;
serviceURL = nil;
serviceURL = [NSURL URLWithString:@"http://api.twitpic.com/2/upload.json"];
oRequest = [[OAMutableURLRequest alloc] initWithURL:serviceURL
                                               consumer:consumer_
                                                  token:accessToken_
                                                  realm:@"http://api.twitter.com/"
                                      signatureProvider:nil];
[oRequest setHTTPMethod:@"POST"];
[oRequest setValue:@"https://api.twitter.com/1/account/verify_credentials.json" forHTTPHeaderField:@"X-Auth-Service-Provider"];
[oRequest setValue:oauthHeader forHTTPHeaderField:@"X-Verify-Credentials-Authorization"];

You should also make this change in OAMutableURLRequest.m at the end of the method - (void)prepare:

 NSString *oauthHeader = [NSString stringWithFormat:@"OAuth realm=\"%@\", oauth_consumer_key=\"%@\", %@oauth_signature_method=\"%@\", oauth_signature=\"%@\", oauth_timestamp=\"%@\", oauth_nonce=\"%@\", oauth_version=\"1.0\"%@",
                         [realm URLEncodedString],
                         [consumer.key URLEncodedString],
                         oauthToken,
                         [[signatureProvider name] URLEncodedString],
                         [signature URLEncodedString],
                         timestamp,
                         nonce,
                         extraParameters];
if(![self valueForHTTPHeaderField:@"X-Verify-Credentials-Authorization"])
    [self setValue:oauthHeader forHTTPHeaderField:@"Authorization"];