SharePoint 2013 - App Store: Time out na validação de segurança

Eventos:

a.) Na interface do SharePoint

Sorry, something went wrong
The security validation for this page has timed out. Click Back in your Web browser, refresh the page, and try your operation again.

b.) Nos logs ULS do SharePoint

1. Sending Request to Office.com with the following URL:http://office.microsoft.com/client/15/app/ [...]

2. Request to office.com with the following URL:https://office.microsoft.com/client/15/appinstallinfo/query?cmu= [...] caused an exception. System.Net.WebException: The remote server returned an error: (400) Bad Request.     at System.Net.HttpWebRequest

3. Microsoft.SharePoint.SPException: Sorry, we can't seem to connect to the SharePoint Store. Try again in a bit.    at Microsoft.SharePoint.Marketplace.OfficeProxy.OfficeProxy.GetAppDownloadStream(String billingMarket, String contentMarket, String rawXMLEntitlementToken, Stream& appDownloadStream, Int64& appStreamLength, String& responseUrl)     at Microsoft.SharePoint.ApplicationPages.StorefrontBase.StartDownload(Guid productId, String oauthAppId, Boolean isUpgrade)     at Microsoft.SharePoint.ApplicationPages.StorefrontBase.AppDownload(Boolean isUpgrade, Boolean autoRedirect)     at Microsoft.SharePoint.ApplicationPages.StorefrontBase.PostHug()     at Microsoft.SharePoint.ApplicationPages.StorefrontBase.Render(HtmlTextWriter writer)     at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)     at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Solução:

Adicione o endereço https://*.microsoft.com na zona das paginas confiáveis nas configurações de internet para cada conta de serviço que executam os applications pools dos service applications:
1. App Management Service Application
2. Microsoft SharePoint Foundation Subscription Settings Service Application.