Device Verification: Display the "The other party cancelled the verification." modal

Riot/Modules/DeviceVerification/Verify/DeviceVerificationVerifyViewController.swift

@@ -175,7 +175,11 @@ final class DeviceVerificationVerifyViewController: UIViewController {
     }
 
     private func renderCancelled(reason: MXTransactionCancelCode) {
-        // TODO
+        self.activityPresenter.removeCurrentActivityIndicator(animated: true)
+
+        self.errorPresenter.presentError(from: self, title: "", message: VectorL10n.deviceVerificationCancelled, animated: true) {
+            self.viewModel.process(viewAction: .cancel)
+        }
     }
 
     private func renderCancelledByMe(reason: MXTransactionCancelCode) {

Riot/Modules/DeviceVerification/Verify/DeviceVerificationVerifyViewModel.swift

@@ -66,21 +66,26 @@ final class DeviceVerificationVerifyViewModel: DeviceVerificationVerifyViewModel
     func process(viewAction: DeviceVerificationVerifyViewAction) {
         switch viewAction {
         case .confirm:
-            self.confirm()
+            self.confirmTransaction()
         case .complete:
             self.coordinatorDelegate?.deviceVerificationVerifyViewModelDidComplete(self)
         case .cancel:
+            self.cancelTransaction()
             self.coordinatorDelegate?.deviceVerificationVerifyViewModelDidCancel(self)
         }
     }
     
     // MARK: - Private
     
-    private func confirm() {
+    private func confirmTransaction() {
         self.update(viewState: .loading)
 
         self.transaction.confirmSASMatch()
     }
+
+    private func cancelTransaction() {
+        self.transaction.cancel(with: MXTransactionCancelCode.user())
+    }
     
     private func update(viewState: DeviceVerificationVerifyViewState) {
         self.viewDelegate?.deviceVerificationVerifyViewModel(self, didUpdateViewState: viewState)