using Microsoft.SharePoint.Client; using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Security; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace UpdateMasterPage { public partial class UpdateMasterPage: System.Windows.Forms.Form { public UpdateMasterPage () { InitializeComponent(); } private SecureString ConvertToSecureString(string password) { if (password == null) throw new ArgumentNullException("password"); var securePassword = new SecureString(); foreach (char c in password) securePassword.AppendChar(c); securePassword.MakeReadOnly(); return securePassword; } private void button1_Click(object sender, EventArgs e) { Microsoft.SharePoint.Client.ClientContext cc = new Microsoft.SharePoint.Client.ClientContext("https://Gowtha.pnpdemo.com/"); SecureString secstring = ConvertToSecureString(“********”); SharePointOnlineCredentials creds = new SharePointOnlineCredentials("gowtham@pnp.onmicrosoft.com", secstring); // The SharePoint web at the URL. Web web = cc.Web; // We want to retrieve the web's properties. cc.Load(web); // Execute the query to the server. cc.ExecuteQuery(); var a = web.Title; // For debug checks. var master = web.CustomMasterUrl; // For debug checks. web.CustomMasterUrl = "/_catalogs/masterpage/seattle.master"; // Or the original page desired. web.MasterUrl = "/_catalogs/masterpage/seattle.master"; web.Update(); // Execute the query to server. cc.ExecuteQuery(); } }