RestKit Customize Serialization - iphone

Question

I need to configure RestKit to interact with a server API that expects the following:
All requests are in multipart/form-data
There is a JSON payload. However the client must collapse the payload
into a form-data string and prepend it with "json="
Authentication is done via hashing the contents of JSON payload with
the URL including any GET parameters. And appending this hash to URL (Yes I know this is bad. But I
have no control over the API)
I'm trying to get RestKit append its serialization output to a json=, then modify the RKObjectLoader to computer and append the correct signature hash.
I've tried subclassing RKObjectManager and overriding sendObject:toResourcePath:usingBlock: to override the HTTPBody; but can't get this to work. I've also tried subclassing RKClient's and configureRequest: but it seems like this method gets called before object serialization.
This is my first day working with RestKit. Help would be much appreciated! Thanks!

Answer 1

Update: I've worked out a different solution than my original described bottom. I've created a subclasses of RKObjectLoader and RKObjectManager. The custom object manager simply has one change to return the custom object loader. The object loader's send message was overridden to perform custom construction.
Here's a solution I've worked out.
I use a subclass of RKClient where I override
- (void)configureRequest:(RKRequest *)request {
[super configureRequest:request];
request.delegate = self;
}
And do all my encoding/signing in the delegate.
- (void)requestWillPrepareForSend:(RKRequest *)request {
[self encodeJSONPayloadForRequest:request];
[self signRequest:request];
}
- (void)encodeJSONPayloadForRequest:(RKRequest*)request {
NSDictionary * bodyDict = (NSDictionary*)request.params;
NSError * error = nil;
NSString * jsonString = [bodyDict JSONStringWithOptions:JKSerializeOptionNone error:&error];
if (error) NSAssert(false, #"error serializing into JSON");
NSDictionary * dictionary = [NSDictionary dictionaryWithObject:jsonString forKey:#"json"];
request.params = dictionary;
}
I'll need to implement a mechanism for passing through to any pre-existing delegate. However, this approach seems to do the trick.