c# - why Request.IsAuthenticated return true but session is null -

in asp.net mvc project. use area named office.

 area |--office      |--controllers            |--accountcontroller                  |-- methods: index (authorized)  controllers |--homecontroller      |-- methods: index (not required authorized) 

share folder in project(not in area) contains: _loginpartial.chtml, _layout.chtml (use _loginpartial.chtml)

this code in _loginpartial.chtml:

@if (request.isauthenticated) {     <div class="dropdown">         <span data-toggle="dropdown">             <span><b>hello</b></span>             <span><b>@user.identity.name</b></span>         </span>         <ul class="dropdown-menu" role="menu" aria-labelledby="dlabel">             <li role="presentation">                 <a role="menuitem" tabindex="-1" href="/office/account/password">change password</a>             </li>         </ul>     </div>     <span>.</span>     using (html.beginform("logoff", "home", formmethod.post, new { id = "logoffform" })) {         @html.antiforgerytoken()     <a href="javascript:document.getelementbyid('logoffform').submit()">exit</a>     } } else {     <text>log in</text> } 

i use method session of user , if session null, redirect login page. code in basecontroller

protected account account {         {          bool flag = true;          if (session["user"] == null)              flag = this.relogin();           if (flag == false) return null;           account account = (account)session["user"];          return account;                  } }  protected bool relogin() {     httpcookie cookieusername = request.cookies["username"];     if (cookieusername == null)         return false;      httpcookie cookiepassword = request.cookies["password"];     if (cookiepassword == null)         return false;      string username = cookieusername.value;     string password = cookiepassword.value;     account account = this.loginwithencrypt(username, password);     this.setsession(account);      return account != null; }  private void setsession(account account) {     if (account == null || account.issuspend == true)         return;      session["user"] = account;      this.setcookie("username", account.code);     this.setcookie("password", account.password);  }  protected account login(string username, string password) {     accountbl accountbl = new accountbl();     account account = accountbl.loadbycodeandpassword(username, password);     this.setsession(account);      return account; }  protected void logout() {     formsauthentication.signout();     session["user"] = null;      this.removecookie("username");     this.removecookie("password"); } 

this code login in homecontroller (inherited basecontroller) in office area:

[httppost] public actionresult login(string username, string password, string returnurl) {     account account = this.login(username, password);      if (account == null)     {          viewbag.error = "1";          return view();     }     else     {          formsauthentication.setauthcookie(account.code, true);           if (string.isnullorwhitespace(returnurl))              return redirecttoaction("index");          else              return redirect(returnurl);     } } 

i go localhost/home/index, display username. after that, go localhost/office/account/index, said i'm not log in redirect me login page.
my question: if request.isauthenticated true, session null. has wrong , cannot figure out.
i try set formsauthentication.setauthcookie(account.code, true) , when log out, remove cookie , set formsauthentication.signout. doesn't work.
my target: if show username, user have session on site.

if doesn't clear you, please comment below , edit it.

thanks