swift JSON calls, closures using usergrid IOS SDK and multiple calls

Question

I am using Xcode 8.2.1 for an IOS app, the latest usergrid SDK 2.1.3. I am having troubles with the best way to make multiple calls to usergrid to validate data before finally creating a new entity. The problem is the code is continuing before the validation on 1 or more users is complete. The validation MUST happen before I have add the users to the entity that I want to create.

Usergrid has the following performRequest for all Data calls :

    func performRequest(_ request:UsergridRequest, completion:UsergridResponseCompletion?) {
        session.dataTask(with: request.buildNSURLRequest()) { [weak self] (data, response, error) -> Void in
            let usergridResponse = UsergridResponse(client:self?.client, data: data, response: response as? HTTPURLResponse, error: error as NSError?)
            DispatchQueue.main.async {
                completion?(usergridResponse)
            }
        }.resume()
    }
}

The completion handler returns too late. (Very common theme).

I want to do this : - with a list of users, check whether they exist already. Usergrid API: UsergridUser.checkAvailable - Add user if they don't exist - Create a new group - Add the users to the new group

static func checkAvailabilty(username:String, email:String, completion: @escaping (AuthResult) -> ()) {
//
// other checking
//  error: UsergridResponseError?

UsergridUser.checkAvailable(email, username: username, completion: { (error,avail) -> Void in
    if error != nil {
        completion(.failure(error))
    } else {
        completion(.success(avail))
    }
  })
}

And in the View controller :

UsergridManager.checkAvailabilty(username: "jim", email: "") { result in
    switch result {
    case .success(let granted) :
        if granted {
            print("user is available")
        } else {
            print("user is NOT available")
        }
    case .failure(let error): print(error?.errorDescription)
    }

}

The View controller continue's before I know whether the user is available. Should the performRequest be changed? I have attempted DispatchGroup, attempted a Dispatch.main.sync - but would like another option rather than nesting the completion handlers for all these calls.