How can i access a web.config key in javascript. There is complex javascript function already written in a .js file and I need to add a value associated with the key - AUTHENTICATION_FLAG in a javascript function. I am coding this in C#.  --- > ConfigurationManager.AppSettings["AUTHENTICATION_FLAG"]

Thank you in advance 

You need to read it in the codeBehind to a protected variable like

protected string strAppTitle = ConfigurationSettings.AppSettings["AppTitle"];

Then in the JavaScript, you can use

var strAppTitle = "<%=strAppTitle%>" ;