title: Logout if session expires from no activity and redirect to login page
body: <p>I'm trying to update a website with flask where users have accounts and are able to login. I want to make user session expire and logout if there is no activity for more than 10 mins and redirect the user to the login page.</p>
  <p>I want to update it in <code>@app.before_request</code> and below is my code. How do I check for the login time and check if there has been no activity, then logout.</p>
  <pre><code>@app.before_request
  def look_for_user(user=None):
          g.usr = {}
      g.api = False
      if user:
          g.usr = user
      if 'user_id' in session:
          g.usr = get_user((session['user_id'])) //from db
          if not g.usr:
              g.usr = {}
      if not g.usr:
          if request.url_rule:
              if request.url_rule.rule not in app.config['LOGIN_NOT_REQUIRED']:
                  session['postlogin_landing_page'] = request.path
                  if g.api:
                      return jsonify(error=True, error_message='Invalid Login/Token')
                  else:
                      return redirect(app.config['LOGIN_URL'])
      elif 'login_page' in session and request.url_rule:
          if request.url_rule.rule not in app.config:
              landing_page = session.pop('login_page')
              return redirect(landing_page)
  </code></pre>