Get first response object in PromiseKit then done block

I'm calling three services in a row. When I'm calling third service, I need to use variable from first service response which is userModel. I can get second service response from which is initModel but can't reach first model userModel. My Question is that how can I use userModel in done block by returning it then blocks?

P.S: I tried to return -> Promise<(UserModel,InstallationModel)> in first call but because UserModel is already an object not a promise, I need to convert it to promise to return it. This looks like me a bad way to do it.

As you can see I'm storing it with self.userModel = userModel which I don't wanna do.

func callService(completionHandler: @escaping (Result<UserModel>) -> Void) {
    SandboxService.createsandboxUser().then { userModel -> Promise<InstallationModel> in
        self.userModel = userModel
        return SandboxService.initializeClient(publicKey: self.keyPairs.publicKey)
    }.then { initModel -> Promise<DeviceServerResponseModel> in
        self.initModel = initModel
        if let unwrappedUserModel = self.userModel {
            return SandboxService.deviceServerServiceCaller(authKey: initModel.token.token,apiKey:unwrappedUserModel.apiKey,privaKey: self.keyPairs.privateKey)
        }
        throw ServiceError.handleParseError()
    }.then { serverResponseModel -> Promise<UserModel> in
        if let unwrappedInitModel = self.initModel, let unwrappedUserModel = self.userModel {
            return SandboxService.sessionServiceCaller(authKey: unwrappedInitModel.token.token, apiKey: unwrappedUserModel.apiKey, privaKey: self.keyPairs.privateKey)
        }
        throw ServiceError.handleParseError()
    }.done { userModel in
        completionHandler(Result.success(userModel))
    }.catch { error in
        completionHandler(Result.error(error))
    }
}

I had also opened issue at PromiseKit page @Github. I'm sharing answer of Mxcl from Github to here also.

func callService(completionHandler: @escaping (Result<UserModel>) -> Void) {
    SandboxService.createsandboxUser().then { userModel in
        firstly {
            SandboxService.initializeClient(publicKey: self.keyPairs.publicKey)
        }.then { initModel in
            SandboxService.deviceServerServiceCaller(authKey: initModel.token.token, apiKey: userModel.apiKey,privaKey: self.keyPairs.privateKey).map{ ($0, initiModel) }
        }.then { serverResponseModel, initModel in
            SandboxService.sessionServiceCaller(authKey: initModel.token.token, apiKey: userModel.apiKey, privaKey: self.keyPairs.privateKey)
        }
    }.pipe(to: completionHandler)
}