可能有人知道Cookie的生成由machineKey有关，machineKey用于决定Cookie生成的算法和密钥，并如果使用多台服务器做负载均衡时，必须指定一致的machineKey用于解密，那么这个过程到底是怎样的呢？
如果需要在.NET Core中使用ASP.NET Cookie，本文将提到的内容也将是一些必经之路。
抽丝剥茧，一步一步分析
首先用户通过AccountController->Login进行登录：
// // POST: /Account/Login public async Task<ActionResult> Login(LoginViewModel model, string returnUrl) { if (!ModelState.IsValid) { return View(model); } var result = await SignInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, shouldLockout: false); switch (result) { case SignInStatus.Success: return RedirectToLocal(returnUrl); // ......省略其它代码 } }
它调用了SignInManager的PasswordSignInAsync方法，该方法代码如下（有删减）：
public virtual async Task<SignInStatus> PasswordSignInAsync(string userName, string password, bool isPersistent, bool shouldLockout) { // ...省略其它代码 if (await UserManager.CheckPasswordAsync(user, password).WithCurrentCulture()) { if (!await IsTwoFactorEnabled(user)) { await UserManager.ResetAccessFailedCountAsync(user.Id).WithCurrentCulture(); } return await SignInOrTwoFactor(user, isPersistent).WithCurrentCulture(); } // ...省略其它代码 return SignInStatus.Failure; }
想浏览原始代码，可参见官方的Github链接：
可见它先需要验证密码，密码验证正确后，它调用了SignInOrTwoFactor方法，该方法代码如下：
private async Task<SignInStatus> SignInOrTwoFactor(TUser user, bool isPersistent) { var id = Convert.ToString(user.Id); if (await IsTwoFactorEnabled(user) && !await AuthenticationManager.TwoFactorBrowserRememberedAsync(id).WithCurrentCulture()) { var identity = new ClaimsIdentity(DefaultAuthenticationTypes.TwoFactorCookie); identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, id)); AuthenticationManager.SignIn(identity); return SignInStatus.RequiresVerification; } await SignInAsync(user, isPersistent, false).WithCurrentCulture(); return SignInStatus.Success; }
该代码只是判断了是否需要做双重验证，在需要双重验证的情况下，它调用了AuthenticationManager的SignIn方法；否则调用SignInAsync方法。SignInAsync的源代码如下：
public virtual async Task SignInAsync(TUser user, bool isPersistent, bool rememberBrowser) { var userIdentity = await CreateUserIdentityAsync(user).WithCurrentCulture(); // Clear any partial cookies from external or two factor partial sign ins AuthenticationManager.SignOut(DefaultAuthenticationTypes.ExternalCookie, DefaultAuthenticationTypes.TwoFactorCookie); if (rememberBrowser) { var rememberBrowserIdentity = AuthenticationManager.CreateTwoFactorRememberBrowserIdentity(ConvertIdToString(user.Id)); AuthenticationManager.SignIn(new AuthenticationProperties { IsPersistent = isPersistent }, userIdentity, rememberBrowserIdentity); } else { AuthenticationManager.SignIn(new AuthenticationProperties { IsPersistent = isPersistent }, userIdentity); } }
可见，最终所有的代码都是调用了AuthenticationManager.SignIn方法，所以该方法是创建Cookie的关键。
AuthenticationManager的实现定义在Microsoft.Owin中，因此无法在ASP.NET Identity中找到其源代码，因此我们打开Microsoft.Owin的源代码继续跟踪（有删减）：
public void SignIn(AuthenticationProperties properties, params ClaimsIdentity[] identities) { AuthenticationResponseRevoke priorRevoke = AuthenticationResponseRevoke; if (priorRevoke != null) { // ...省略不相关代码 AuthenticationResponseRevoke = new AuthenticationResponseRevoke(filteredSignOuts); } AuthenticationResponseGrant priorGrant = AuthenticationResponseGrant; if (priorGrant == null) { AuthenticationResponseGrant = new AuthenticationResponseGrant(new ClaimsPrincipal(identities), properties); } else { // ...省略不相关代码 AuthenticationResponseGrant = new AuthenticationResponseGrant(new ClaimsPrincipal(mergedIdentities), priorGrant.Properties); } }
AuthenticationManager的Github链接如下：https://github.com/aspnet/AspNetKatana/blob/c33569969e79afd9fb4ec2d6bdff877e376821b2/src/Microsoft.Owin/Security/AuthenticationManager.cs
可见它用到了AuthenticationResponseGrant，继续跟踪可以看到它实际是一个属性：
public AuthenticationResponseGrant AuthenticationResponseGrant { // 省略get set { if (value == null) { SignInEntry = null; } else { SignInEntry = Tuple.Create((IPrincipal)value.Principal, value.Properties.Dictionary); } } }
发现它其实是设置了SignInEntry，继续追踪：