You can store a value within the current Request such that it will be accessible within the Response.
In your case, on successful login, set countdown timer(example: 60) in response and add it to header of response as below.
Add below code after authenticating user and before redirecting user to next page.
This will add Count down timer value to your Response within Dashboard.aspx by simply checking the appropriate header value as below:
if(Request.Headers["YourCountdownTimerValue"] != null)
int passedValue = Convert.ToInt32(Reqeuest.Headers["YourCountdownTimerValue"]);
On Dashboard.aspx page, you can assign value of
Now, again, if user navigates to other page, you can write this value as header of request and get value of this variable in new page as above.
Simple.!! Hope it makes sense to you.