These days I’ve been working on an auto hosted app for SharePoint (office 365 actually).
I had to grant an anonymous access to one of the pages without requiring clients to give anonymous access to their SharePoint site. But I still needed to read a few properties from the App Web web site (the SPWeb provisioned by SharePoint when installing an app)
I had to play around a lot but I finally found the solution:
//uri of the app web, you can pass this url via a query string parameter
var targetUrl = new Uri("https://<tenantname>-<appinstallationid>.sharepoint.com/<appname>");
var token = TokenHelper.GetAppOnlyAccessToken(TokenHelper.SharePointPrincipal, targetUrl.Authority, TokenHelper.GetRealmFromTargetUrl(targetUrl));
using (var ctx = TokenHelper.GetClientContextWithAccessToken(targetUrl.ToString(), token.AccessToken))
You also need to add the “allow app only calls to SharePoint” in the manifest.
I hope it’ll save you a lot of time.