How to Expires access token on sign out?

Thanks for replying.

Okay, let me try to explain with some code.

  public ActionResult Index()
        {
            if (Session["access_token"] == null)
                return RedirectToAction("Index", "Admin");
         
            return View();
        }

First my app check if there is "access_token" in session, if there is not it will redirect to this link

https://login.windows.net/common/oauth2/authorize?response_type=code&client_id=8c8xxxx-blah-blah-8f4c-xxxxfe3&resource=https%3a%2f%2fanalysis.windows.net%2fpowerbi%2fapi&redirect_uri=http%3a%2f%2flocalhost%3a49424%2fHome%2f.

It will prompt the user to login using their account, then it fill Session["access_token"] with the token from authenticationResult.AccessToken; so they can see power bi reports in my apps. Then there is logout button (see the code below)

 public ActionResult Logout()
        {
            Session.Abandon();
            Session["access_token"] = null;
            return Redirect("https://login.windows.net/common/oauth2/logout");
        }

But if they press back button (go back one page), user still can see the reports. After I debug it, the authenticationContext.AcquireTokenByAuthorizationCodeAsync not prompting user to login again, it automatically filled Session["access_token"] with the token.

I'm not using Azure AD. I registered my app via https://dev.powerbi.com/apps.

Hope you can understand my problem (and my english). Thanks :).