I am able to use an NSMutableURLRequest with an NSURLConnection to connect to a SOAP web service, as follows:

NSString *soapMessage = [NSString stringWithFormat:@"<?xml version=\"1.0\" encoding=\"utf-8\"?>"
                         "<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">"
                         "<soap:Body>"
                         "<CelsiusToFahrenheit xmlns=\"http://www.w3schools.com/webservices/\">"
                         "<Celsius>140.0</Celsius>"
                         "</CelsiusToFahrenheit>"
                         "</soap:Body>"
                         "</soap:Envelope>"];

NSData *soapData = [soapMessage dataUsingEncoding:NSUTF8StringEncoding];
NSURL *url = [NSURL URLWithString:@"http://w3schools.com/webservices/tempconvert.asmx"];
NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:url];
NSString *msgLength = [NSString stringWithFormat:@"%lu", (unsigned long)[soapMessage length]];

[theRequest addValue: @"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"];
[theRequest addValue: @"http://www.w3schools.com/webservices/CelsiusToFahrenheit" forHTTPHeaderField:@"SOAPAction"];
[theRequest addValue:@"www.w3schools.com" forHTTPHeaderField:@"Host"];
[theRequest addValue: msgLength forHTTPHeaderField:@"Content-Length"];
[theRequest setHTTPMethod:@"POST"];
[theRequest setHTTPBody:soapData];

How could I do the same using AFNetworking or STHTTPRequest?

STHTTPRequest

//create request
STHTTPRequest *request = [STHTTPRequest requestWithURL:url];
//set header here
[request setHeaderWithName:@"Host" value:@"www.w3schools.com"];
[request setHeaderWithName:@"SOAPAction" value: @"http://www.w3schools.com/webservices/CelsiusToFahrenheit"];
[request setHeaderWithName:@"Content-Type" value:@"text/xml; charset=utf-8"];
//set body here
request.rawPOSTData = soapData;

//completion block
request.completionBlock = ^(NSDictionary *headers, NSString *body) {
    NSLog(@"headers = %@\nbody = %@", headers, body);

    //parse xml string object here as request is successfull
    if (body.length > 0) 
    {
       NSError *error= nil;
       NSDictionary *dict = [XMLReader dictionaryForXMLString:body error:&error];
       if (!error) 
       {
         NSLog(@"XML Dictionary: %@",dict);
         //do necessary requirement here
       }
       else
         NSLog(@"Error while parsing xml data : %@",[error description]);

    }
    else
      NSLog(@"No response from request");
};

//error block
request.errorBlock = ^(NSError *error) {
    NSLog(@"%@",[error description]);
};

//start request
[request startAsynchronous];

---

AFNetworking

AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:theRequest];

operation.responseSerializer = [AFXMLParserResponseSerializer serializer];

[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

    //parse NSXMLParser object here if request successfull
    if ([responseObject isKindOfClass:[NSXMLParser class]]) {
        NSXMLParser *parser = (NSXMLParser *)responseObject;
        NSDictionary *dict = [XMLReader dictionaryForNSXMLParser:parser];
        NSLog(@"JSON: %@ : %@", responseObject,dict);
    }
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"Error: %@", error);
}];
[[NSOperationQueue mainQueue] addOperation:operation];

Here XMLReader provides NSDictionary of XMLData using NSXMLParser

I haved added one more method in XMLReader classes :

+(NSDictionary*)dictionaryForNSXMLParser:(NSXMLParser*)parser error:(NSError **)error

EDIT : Method Description

+ (NSDictionary *)dictionaryForNSXMLParser:(NSXMLParser *)xmlParser error:(NSError **)error
{
  XMLReader *reader = [[XMLReader alloc] initWithError:error];
  NSDictionary *rootDictionary = [reader objectWithNSXMLParser:xmlParser options:0];
  return rootDictionary;
}

---

objectWithNSXMLParser method.

- (NSDictionary *)objectWithNSXMLParser:(NSXMLParser *)xmlParser options:(XMLReaderOptions)options
{
  // Clear out any old data
  self.dictionaryStack = [[NSMutableArray alloc] init];
  self.textInProgress = [[NSMutableString alloc] init];

  // Initialize the stack with a fresh dictionary
  [self.dictionaryStack addObject:[NSMutableDictionary dictionary]];

  [xmlParser setShouldProcessNamespaces:(options & XMLReaderOptionsProcessNamespaces)];
  [xmlParser setShouldReportNamespacePrefixes:(options & XMLReaderOptionsReportNamespacePrefixes)];
  [xmlParser setShouldResolveExternalEntities:(options & XMLReaderOptionsResolveExternalEntities)];

  xmlParser.delegate = self;
  BOOL success = [xmlParser parse];

  // Return the stack's root dictionary on success
  if (success)
  {
    NSDictionary *resultDict = [self.dictionaryStack objectAtIndex:0];
    return resultDict;
  }

  return nil;
}