I suggest using an OAuth library to handle the OAuth signature generation. It can be a pain in the ass to wrangle the Authorization header. I've used oauthconsumer with success.
Code sample:
OAConsumer *consumer = [[OAConsumer alloc] initWithKey:oauthConsumerKey secret:oauthConsumerSecret];
OAToken *token = [[OAToken alloc] initWithKey:oauthAccessToken secret:oauthAccessTokenSecret];
OAHMAC_SHA1SignatureProvider *provider = [[OAHMAC_SHA1SignatureProvider alloc] init];
OAMutableURLRequest *request = [[OAMutableURLRequest alloc] initWithURL:[NSURL URLWithString:urlString] consumer:consumer token:token realm:nil signatureProvider:provider];
[request prepare];
NSHTTPURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
In this example, the 5 strings you will provide are:
oauthConsumerKey
oauthConsumerSecret
oauthAccessToken
oauthAccessTokenSecret
urlString