RKObjectManager, NSDictionary parameters.
NSDictionary *params = @{@"param1" : @"value1",
@"param2" : @"value2",
@"param3" : @"value3"};
[[RKObjectManager sharedManager] getObject:someObject path:nil parameters:params success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
} failure:^(RKObjectRequestOperation *operation, NSError *error) {
}]