Office 365 SharePoint/OneDrive REST API snippet.

HomeController.cs

public ActionResult Stats()
        {
            var authorizationEndpoint = "https://login.windows.net/";
            var resource = "https://graph.windows.net";
            //Change port number to whatever your Visual Studio has chosen for you
            var redirectURI = "https://localhost:44300/Home/CatchCode";

            string authorizationUrl = string.Format("{0}{1}/oauth2/authorize?&response_type=code&client_id={2}&resource={3}&redirect_uri={4}", 
                authorizationEndpoint, 
                ClaimsPrincipal.Current.FindFirst(TenantIdClaimType).Value, 
                AppPrincipalId, 
                resource, 
                redirectURI);

            return Redirect(authorizationUrl);
        }

        public async Task<ActionResult> CatchCode(string code)
        {            
            var tenantId = ClaimsPrincipal.Current.FindFirst(TenantIdClaimType).Value;
            var appRedirect = "https://localhost:44300/Home/CatchCode";
            //Replace these variables with details from your tenant
            var sharepointUrl = "https://contoso-my.sharepoint.com/";
            var sharepointUsername = "andreas_contoso_onmicrosoft_com";

            AuthenticationContext authContext = new AuthenticationContext(String.Format(CultureInfo.InvariantCulture, LoginUrl, tenantId));
            ClientCredential credential = new ClientCredential(AppPrincipalId, AppKey);
            var assertionCredential = authContext.AcquireTokenByAuthorizationCode(code, new Uri(appRedirect), credential);
                                 
            string authHeader = string.Empty;
            if (assertionCredential.IsMultipleResourceRefreshToken)
            {
                AuthenticationResult arSP = authContext.AcquireTokenByRefreshToken(assertionCredential.RefreshToken, AppPrincipalId, credential, sharepointUrl);
                authHeader = arSP.CreateAuthorizationHeader();
            }

            var skyGetAllFilesCommand = sharepointUrl +
            "/personal/" +
            sharepointUsername +
            "/_api/web/GetFolderByServerRelativeUrl('/personal/"+ 
            sharepointUsername +
            "/Documents/Shared%20with%20Everyone')/Files";

            HttpClient client = new HttpClient();
            HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Get, skyGetAllFilesCommand);
            request.Headers.TryAddWithoutValidation("Authorization", authHeader);
            HttpResponseMessage response = await client.SendAsync(request);
            string responseString = await response.Content.ReadAsStringAsync();            

            ViewBag.skyResponse = responseString;

            return View();            
        }