How to Get SharePoint Client Context in SharePoint Apps (Provider Hosted / SharePoint Access ) in CSOM (Client Side Object Model)

http://www.codeproject.com/Articles/581060/HowplustoplusGetplusSharePointplusClientplusContex

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Introduction

The first step of app development is to correctly get access to SharePoint client context. I have struggled to develop a simple model to initialize the SharePoint Client context. Most of the App development includes ASP Master pages. So I need to figure out a working model for app development.

First, you need to know how SharePoint offers the

contextString

.

contextString

offers when SharePoint gets redirected from appredirect.aspx URL.

Example: https://rajee.sharepoint.com/_layouts/15/appredirect.aspx?instance_id={B0D5D768-303F-4AE7-A4D3-F94B687C6AB3

At that point, we need to capture the

contextString

and generate either AccessTokenor RefreshToken and save it for accessing the SharePoint Client Context at a later time. Otherwise, it will result in generating the error The parameter 'token' cannot be a null or empty string (This is a nasty error which drove me crazy.).

Normally

AccessToken

is valid for 12 hours and

RefreshToken

is valid for 6 months.

In my approach, I used another key which is called as

CacheKey

to identify the user uniquely. Therefore I use this value to maintain a cookie based on the user.

Reference: Tips and FAQs: OAuth and remote apps for SharePoint 2013





The following shows my approach to do this. If you have a master page, you need to put the code in the

onInit()

rather than page load.


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protected void Page_Load(object sender, EventArgs e)
{
var key = Session["CashKey"];

// sharepoint url (app hosted url)
var hostWeb = Page.Request["SPHostUrl"];

// Sharepoint url with app Title (app deployed sp url)
Uri SharePointUri = new Uri(hostWeb + "/SharePointApp1/");

// This is first time the app is running
if (key == null)
{
// get the TokenString
var contextTokenString = TokenHelper.GetContextTokenFromRequest(Page.Request);
// Get the contexttoken by passing the token string
var contextToken = TokenHelper.ReadAndValidateContextToken
(contextTokenString, Request.Url.Authority);

//Since some browsers does not support cookie name more than 40 chars
// Im taking first 40 chars
var cookieName = contextToken.CacheKey.Substring(0, 40);

//Add User specific cookie name to the Session
Session.Add("CashKey", cookieName);

// Get the Refresh Token
var refreshToken = contextToken.RefreshToken;
// Add the cookie value (refresh Token)
Response.Cookies.Add(new HttpCookie(cookieName, refreshToken));

}
else
{
// USER already in the application,  means it is not getting redirect from the appRedirect
// So contextstring is null
}
}

This is code for button click.


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protected void Button1_Click(object sender, EventArgs e)
{
// sharepoint url (app hosted url)
var hostWeb = Page.Request["SPHostUrl"];

// Sharepoint url with app name (app deployed sp url)
Uri SharePointUri = new Uri(hostWeb + "/SharePointApp1/");

// Get the cookie name from the session
var key = Session["CashKey"] as string;
// Get the refresh token from the cookie
var refreshToken = Request.Cookies[key].Value;

//Get the access Token By passing refreshToken
// 00000003-0000-0ff1-ce00-000000000000 is principal name for SP2013 it is unique
var accessToken = TokenHelper.GetAccessToken(refreshToken,
"00000003-0000-0ff1-ce00-000000000000",
SharePointUri.Authority, TokenHelper.GetRealmFromTargetUrl(SharePointUri));

// Access the Sharepoint Do your work
using (var clientContext = TokenHelper.GetClientContextWithAccessToken
("https://rajee.sharepoint.com/SharepointApp1", accessToken.AccessToken))
{
clientContext.Load(clientContext.Web, web => web.Title);
clientContext.ExecuteQuery();
Response.Write(clientContext.Web.Title);
}
}

Note: In the middle of the app, if the context is broken due to expiration or some other case you need to initialize the app from the AppRedirect, therefore you can:


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var hostWeb = Page.Request["SPHostUrl"];
var val = TokenHelper.GetAppContextTokenRequestUrl(hostWeb, Server.UrlEncode(Request.Url.ToString()));