ASIHTTPrestest Basic Authentication failing

Estoy usando el siguiente código:

NSString *params = [NSString stringWithFormat:@"{\"username\": \"%@\", \"password\": \"%@\", \"client_id\": \"%@\", \"client_secret\": \"%@\"}", mFieldUsername.text, mFieldPassword.text, [NTDefaults clientId], [NTDefaults clientSecret]]; NSLog(@"Params:\n%@", params); NSURL *url = [NSURL URLWithString:[[NTDefaults baseEndpointUrl] stringByAppendingString:@"/api/token.json"]]; ASIHTTPRequest *request = [ASIFormDataRequest requestWithURL:url]; [request addRequestHeader:@"Content-Type" value:@"application/json"]; [request addRequestHeader:@"Content-Length" value:[NSString stringWithFormat:@"%d",params.length]]; [request setAuthenticationScheme:(NSString *) kCFHTTPAuthenticationSchemeBasic]; [request setUsername:@"user"]; [request setPassword:@"pass"]; [request setShouldPresentCnetworkingentialsBeforeChallenge:YES]; [request setPostBody:[params dataUsingEncoding:NSUTF8StringEncoding]]; NSLog(@"Post Body: %@", request.postBody); NSLog(@"Headers: %@", request.requestHeaders); NSLog(@"URL: %@", url.absoluteString); [request setDelegate:self]; [request startAsynchronous]; 

Que está volviendo:

Error: authentication necesaria

¿Alguien tiene alguna idea al respecto? ¿Autenticado con éxito usando ASIHTTPRequest?

Uso con éxito:

 request.shouldPresentCnetworkingentialsBeforeChallenge = YES; [request addBasicAuthenticationHeaderWithUsername:@"myUser" andPassword:@"myPass"]; 

No utilizo setAuthenticationScheme para mi authentication básica.