use this code to authenticate with SharePoint online office 360. string userName = Your user Name; string password = Pasword; string baseurl = "Share point URL"; Uri uri = new Uri(baseurl); var securePassword = new SecureString(); foreach (var c in password) { securePassword.AppendChar(c); } var credentials = new SharePointOnlineCredentials(userName, securePassword); var authCookie = credentials.GetAuthenticationCookie(uri); var fedAuthString = authCookie.TrimStart("SPOIDCRL=".ToCharArray()); if (fedAuthString != null) { result.UserToken = fedAuthString; result.Message = "User has been logged in successfully"; } else { result.Message = "Invalid User!!"; }