Authentication to Office 365 APIs using the Office 365 .NET client library

Office365_AuthHelper.cs

// code to authenticate to Office 365 and obtain a DiscoveryClient object, which can then be used to create 
// a SharePointClient or OutlookServicesClient in order to access files/mail/calendar/contacts etc..

var signInUserId = ClaimsPrincipal.Current.FindFirst(ClaimTypes.NameIdentifier).Value;
var userObjectId = ClaimsPrincipal.Current.FindFirst("http://schemas.microsoft.com/identity/claims/objectidentifier").Value;

// !!! NOTE: DO NOT USE NaiveSessionCache IN PRODUCTION. A MORE PERSISTENT CACHE SUCH AS A DATABASE IS RECOMMENDED FOR PRODUCTION USE !!!!
AuthenticationContext authContext = new AuthenticationContext(SettingsHelper.Authority, new NaiveSessionCache(signInUserId));

DiscoveryClient discClient = new DiscoveryClient(SettingsHelper.DiscoveryServiceEndpointUri,
    async () =>
    {
        var authResult = await authContext.AcquireTokenSilentAsync(SettingsHelper.DiscoveryServiceResourceId,
                                                                   new ClientCredential(SettingsHelper.ClientId,
                                                                                        SettingsHelper.AppKey),
                                                                   new UserIdentifier(userObjectId,
                                                                                      UserIdentifierType.UniqueId));
        return authResult.AccessToken;
    });