The remote server returned an error: (403) Forbidden

The remote server returned an error: (403) Forbidden
Troubleshooting Exceptions: System.Net.WebException
Root Cause: You might have missing SPO Authentication
Solution:

 Check this method in below code: SPOAuthe
 clientContext = SPOAuthe(clientContext);

	using System;
	using Microsoft.SharePoint.Client;
	using SP = Microsoft.SharePoint.Client;
	using System.Security;
	namespace Microsoft.SDK.SharePointServices.Samples
	{
	class RetrieveListItems
	{
	static void Main()
	{
	string siteUrl = "http://MyServer/sites/MySiteCollection";
	ClientContext clientContext = new ClientContext(siteUrl);
	clientContext = SPOAuthe(clientContext);
	SP.List oList = clientContext.Web.Lists.GetByTitle("Announcements");
	CamlQuery camlQuery = new CamlQuery();
	camlQuery.ViewXml = "<View><Query><Where><Geq><FieldRef Name='ID'/>" +
	"<Value Type='Number'>10</Value></Geq></Where></Query><RowLimit>100</RowLimit></View>";
	ListItemCollection collListItem = oList.GetItems(camlQuery);
	clientContext.Load(collListItem);
	clientContext.ExecuteQuery();
	foreach (ListItem oListItem in collListItem)
	{
	Console.WriteLine("ID: {0} \nTitle: {1} \nBody: {2}", oListItem.Id, oListItem["Title"], oListItem["Body"]);
	}
	}
	public static ClientContext SPOAuthe(ClientContext ctx)
	{
	string uname = "MyName";
	string pword = "Password";
	SecureString objSS = new SecureString();
	foreach (char itemC in pword.ToCharArray())
	{
	objSS.AppendChar(itemC);
	}
	ctx.Credentials = new SharePointOnlineCredentials(uname, objSS);
	return ctx;
	}
	}
	}

view raw gistfile1.cs hosted with ❤ by GitHub

Now your code should work..