Spring Security 02 — Basic Introduction Part II

摘要： Spring Security 5.1.4 RELEASE 書接上文，在上一篇中介紹了Spring Security的基本元件以及基本的認證流程，此篇介紹一下Spring Security的一些核心服務。 2 核心服務 Spring Security中還有許多十分重...

Spring Security 5.1.4 RELEASE

書接上文，在上一篇中介紹了Spring Security的基本元件以及基本的認證流程，此篇介紹一下Spring Security的一些核心服務。

2 核心服務

Spring Security中還有許多十分重要的介面，特別是 AuthenticationManager , UserDetailsService 和 AccessDecisionManager ，Spring Security提供了一些實現，使用者亦可自己實現定製的認證授權機制。下面我們來具體看一下幾個介面及Spring Security提供的實現，從而有助於瞭解在認證授權環節中它們的具體作用，以及如何使用。

2.1 AuthenticationManager, ProviderManager and AuthenticationProvider

AuthenticationManger 是一個介面，用來完成認證的邏輯，開發者可按照自己的專案設計需求進行實現。如果，我們希望能夠組合使用多種認證服務，比如基於資料庫和LDAP伺服器的認證服務，Spring Security也是支援的。

ProviderManager 是Spring Security提供的一個實現，但是它本身不處理認證請求，而是將任務委託給一個配置好的 AuthenticationProvider 的列表，其中每一個 AuthenticationProvider 按序確認能否完成認證，每個provider如果認證失敗，會丟擲一個異常，如果認證通過，則會返回一個 Authentication 物件。

AuthenticationManager

AuthenticationManger 是一個介面，其中只有一個方法 authenticate ，用來嘗試對傳入的 Authentication 物件進行認證。

這裡保留了原始碼中的一大段註釋，其中包括了該介面的作用，以及在實現時應當注意的一些問題，這裡不多做敘述，我們目前只需要瞭解這個介面的作用即可，感興趣的同學可以自行閱讀原始碼中的註釋。

/**
 * Processes an {@link Authentication} request.
 *
 * @author Ben Alex
 */
public interface AuthenticationManager {
// ~ Methods
// ========================================================================================================
​
/**
* Attempts to authenticate the passed {@link Authentication} object, returning a
* fully populated <code>Authentication</code> object (including granted authorities)
* if successful.
* <p>
* An <code>AuthenticationManager</code> must honour the following contract concerning
* exceptions:
* <ul>
* <li>A {@link DisabledException} must be thrown if an account is disabled and the
* <code>AuthenticationManager</code> can test for this state.</li>
* <li>A {@link LockedException} must be thrown if an account is locked and the
* <code>AuthenticationManager</code> can test for account locking.</li>
* <li>A {@link BadCredentialsException} must be thrown if incorrect credentials are
* presented. Whilst the above exceptions are optional, an
* <code>AuthenticationManager</code> must <B>always</B> test credentials.</li>
* </ul>
* Exceptions should be tested for and if applicable thrown in the order expressed
* above (i.e. if an account is disabled or locked, the authentication request is
* immediately rejected and the credentials testing process is not performed). This
* prevents credentials being tested against disabled or locked accounts.
*
* @param authentication the authentication request object
*
* @return a fully authenticated object including credentials
*
* @throws AuthenticationException if authentication fails
*/
Authentication authenticate(Authentication authentication)
throws AuthenticationException;
}

ProviderManager

ProviderManager 是 Authentication 的一個實現，並將具體的認證操作委託給一系列的 AuthenticationProvider 來完成，從而可以實現支援多種認證方式。為了幫助閱讀和理解原始碼具體做了什麼，這裡刪除了原來的一部分註釋，並對重要的部分進行了註釋說明。

public class ProviderManager implements AuthenticationManager, MessageSourceAware,
InitializingBean {
​
private static final Log logger = LogFactory.getLog(ProviderManager.class);
​
private AuthenticationEventPublisher eventPublisher = new NullEventPublisher();
private List<AuthenticationProvider> providers = Collections.emptyList();
protected MessageSourceAccessor messages = SpringSecurityMessageSource.getAccessor();
private AuthenticationManager parent;
private boolean eraseCredentialsAfterAuthentication = true;
​
/**
* 用List<AuthenticationProvider>初始化一個ProviderManager
* 也就是上文提到的，ProviderManager將具體的認證委託給不同的provider，從而支援不同的認證方式
*/
public ProviderManager(List<AuthenticationProvider> providers) {
this(providers, null);
}
​
/**
* 也可以為其設定一個父類
*/
public ProviderManager(List<AuthenticationProvider> providers,
AuthenticationManager parent) {
Assert.notNull(providers, "providers list cannot be null");
this.providers = providers;
this.parent = parent;
checkState();
}
​
public void afterPropertiesSet() throws Exception {
checkState();
}
​
private void checkState() {
if (parent == null && providers.isEmpty()) {
throw new IllegalArgumentException(
"A parent AuthenticationManager or a list "
+ "of AuthenticationProviders is required");
}
}
​
/**
* ProviderManager的核心方法，authentication方法嘗試對傳入的Authentication物件進行認證，傳入的Authentication是
* 以使用者的提交的認證資訊，比如使用者名稱和密碼，建立的一個Authentication物件。
* 
* 會依次詢問各個AuthenticationProvider，當provider支援對傳入的Authentication認證，
* 便會嘗試使用該provider進行認證。如果有多個provider都支援認證傳入的Authentication物件，
* 則只會使用第一個支援的provider進行認證。
*
* 一旦有一個provider認證成功了，便會忽略之前任何provider丟擲的異常，之後的provider也不會再
* 繼續認證的嘗試。
*
* 如果所有provider都認證失敗，方法則會丟擲最後一個provider丟擲的異常。
*/
public Authentication authenticate(Authentication authentication)
throws AuthenticationException {
Class<? extends Authentication> toTest = authentication.getClass();
AuthenticationException lastException = null;
AuthenticationException parentException = null;
Authentication result = null;
Authentication parentResult = null;
boolean debug = logger.isDebugEnabled();
​
// 依次使用各個provider嘗試進行認證
for (AuthenticationProvider provider : getProviders()) {
// 如果provider不支援對傳入的Authentication進行認證，則跳過。
if (!provider.supports(toTest)) {
continue;
}
​
if (debug) {
logger.debug("Authentication attempt using "
+ provider.getClass().getName());
}
​
try {
// 呼叫provider的authenticate方法進行認證
result = provider.authenticate(authentication);

// 如果認證成功，則將authentication中使用者的細節資訊複製到result中
// 然後跳出迴圈，不再嘗試後面其他的provider
if (result != null) {
copyDetails(authentication, result);
break;
}
}
catch (AccountStatusException e) {
prepareException(e, authentication);
// 如果待認證的賬號資訊無誤，但是賬號本身異常，比如賬號停用了，則丟擲AccountStatusException異常，
// 並通過prepareException方法，釋出一個AbstractAuthenticationFailureEvent，避免繼續嘗試其他provider進行認證
throw e;
}
catch (InternalAuthenticationServiceException e) {
prepareException(e, authentication);
throw e;
}
catch (AuthenticationException e) {
// 如果該provider認證失敗，捕獲異常AuthenticationException後不丟擲，繼續嘗試下一個provider
// lastException會記錄下最後一個認證失敗的provider丟擲的AuthenticationException異常。
lastException = e;
}
}
​
if (result == null && parent != null) {
// 如果所有provider都沒能認證成功，則交給父類嘗試認證
try {
result = parentResult = parent.authenticate(authentication);
}
catch (ProviderNotFoundException e) {
// 父類如果丟擲該異常不做處理，因為後面有對子類丟擲該異常的處理
}
catch (AuthenticationException e) {
// 父類也沒能認證成功，則最後一個異常為來自父類認證失敗的異常
lastException = parentException = e;
}
}
​
if (result != null) {
if (eraseCredentialsAfterAuthentication
&& (result instanceof CredentialsContainer)) {
// 認證成功，從Authentication中刪除密碼祕鑰等敏感資訊
((CredentialsContainer) result).eraseCredentials();
}
​
// 如果父類認證成功，則會發佈一個AuthenticationSuccessEvent，
// 這一步檢查，防止子類重複釋出
if (parentResult == null) {
eventPublisher.publishAuthenticationSuccess(result);
}

//返回的result為一個Authentication，其中包含了已認證使用者的資訊
return result;

}
​
if (lastException == null) {
lastException = new ProviderNotFoundException(messages.getMessage(
"ProviderManager.providerNotFound",
new Object[] { toTest.getName() },
"No AuthenticationProvider found for {0}"));
}
​
// 如果父類認證失敗，會發佈一個AbstractAuthenticationFailureEvent
// 這一步檢查，防止子類重複釋出
if (parentException == null) {
prepareException(lastException, authentication);
}
​
throw lastException;
}
​
@SuppressWarnings("deprecation")
private void prepareException(AuthenticationException ex, Authentication auth) {
eventPublisher.publishAuthenticationFailure(ex, auth);
}
​
/**
* 從source中複製使用者的資訊到dest
*
* Copies the authentication details from a source Authentication object to a
* destination one, provided the latter does not already have one set.
*
* @param source source authentication
* @param dest the destination authentication object
*/
private void copyDetails(Authentication source, Authentication dest) {
if ((dest instanceof AbstractAuthenticationToken) && (dest.getDetails() == null)) {
AbstractAuthenticationToken token = (AbstractAuthenticationToken) dest;
​
token.setDetails(source.getDetails());
}
}
​
public List<AuthenticationProvider> getProviders() {
return providers;
}
​
public void setMessageSource(MessageSource messageSource) {
this.messages = new MessageSourceAccessor(messageSource);
}
​
public void setAuthenticationEventPublisher(
AuthenticationEventPublisher eventPublisher) {
Assert.notNull(eventPublisher, "AuthenticationEventPublisher cannot be null");
this.eventPublisher = eventPublisher;
}
​
/**
* 設定是否要在認證完成後，讓Authentication呼叫自己的eraseCredentials方法來清除密碼資訊。
*
* If set to, a resulting {@code Authentication} which implements the
* {@code CredentialsContainer} interface will have its
* {@link CredentialsContainer#eraseCredentials() eraseCredentials} method called
* before it is returned from the {@code authenticate()} method.
*
* @param eraseSecretData set to {@literal false} to retain the credentials data in
* memory. Defaults to {@literal true}.
*/
public void setEraseCredentialsAfterAuthentication(boolean eraseSecretData) {
this.eraseCredentialsAfterAuthentication = eraseSecretData;
}
​
public boolean isEraseCredentialsAfterAuthentication() {
return eraseCredentialsAfterAuthentication;
}
​
private static final class NullEventPublisher implements AuthenticationEventPublisher {
public void publishAuthenticationFailure(AuthenticationException exception,
Authentication authentication) {
}
​
public void publishAuthenticationSuccess(Authentication authentication) {
}
}
}

至此可以看到，ProviderManager的認證邏輯還是很簡單清晰的，我們也可以比較清楚理解 AuthenticationManager ， ProviderManager 和 AuthenticationProvider 的關係了。

AuthenticationProvider

AuthenticationProvider 也是一個介面，用來完成具體的認證邏輯。不同的認證方式有不同的實現，Spring Security中提供了多種實現，包括 DaoAuthenticationProvider , AnonymousAuthenticationProvider 和 LdapAuthenticationProvider 等。其中最簡單的 DaoAuthenticationProvider 會在後面介紹，首先來看一下 AuthenticationProvider 的原始碼。同樣的，保留了原始碼中的註釋，感興趣的同學可以細讀，這裡只做簡單的介紹。

可以看到， AuthenticationProvider 中只有2個方法：

• authenticate 完成具體的認證邏輯，如果認證失敗，丟擲AuthenticationException異常

• supports 判斷是否支援傳入的Authentication認證資訊

/**
 * Indicates a class can process a specific
 * {@link org.springframework.security.core.Authentication} implementation.
 *
 * @author Ben Alex
 */
public interface AuthenticationProvider {
// ~ Methods
// ========================================================================================================
​
/**
* Performs authentication with the same contract as
* {@link org.springframework.security.authentication.AuthenticationManager#authenticate(Authentication)}
* .
*
* @param authentication the authentication request object.
*
* @return a fully authenticated object including credentials. May return
* <code>null</code> if the <code>AuthenticationProvider</code> is unable to support
* authentication of the passed <code>Authentication</code> object. In such a case,
* the next <code>AuthenticationProvider</code> that supports the presented
* <code>Authentication</code> class will be tried.
*
* @throws AuthenticationException if authentication fails.
*/
Authentication authenticate(Authentication authentication)
throws AuthenticationException;
​
/**
* Returns <code>true</code> if this <Code>AuthenticationProvider</code> supports the
* indicated <Code>Authentication</code> object.
* <p>
* Returning <code>true</code> does not guarantee an
* <code>AuthenticationProvider</code> will be able to authenticate the presented
* instance of the <code>Authentication</code> class. It simply indicates it can
* support closer evaluation of it. An <code>AuthenticationProvider</code> can still
* return <code>null</code> from the {@link #authenticate(Authentication)} method to
* indicate another <code>AuthenticationProvider</code> should be tried.
* </p>
* <p>
* Selection of an <code>AuthenticationProvider</code> capable of performing
* authentication is conducted at runtime the <code>ProviderManager</code>.
* </p>
*
* @param authentication
*
* @return <code>true</code> if the implementation can more closely evaluate the
* <code>Authentication</code> class presented
*/
boolean supports(Class<?> authentication);
}

DaoAuthenticationProvider

DaoAuthenticationProvider 是Spring Security提供的最簡單的一個 AuthenticationProvider 的實現，也是框架中最早支援的。它使用 UserDetailsService 作為一個DAO來查詢使用者名稱、密碼以及使用者的許可權 GrantedAuthority 。它認證使用者的方式就是簡單的比較 UsernamePasswordAuthenticationToken 中由使用者提交的密碼和通過 UserDetailsService 查詢獲得的密碼是否一致。

下面我們來看一下 DaoAuthenticationProvider 的原始碼，對於原始碼的說明也寫在了註釋中。

DaoAuthenticationProvider 繼承了 AbstractUserDetailsAuthenticationProvider ，而後者實現了 AuthenticationProvider 介面。

public class DaoAuthenticationProvider extends AbstractUserDetailsAuthenticationProvider {
​
/**
* The plaintext password used to perform
* PasswordEncoder#matches(CharSequence, String)}on when the user is
* not found to avoid SEC-2056.
*/
private static final String USER_NOT_FOUND_PASSWORD = "userNotFoundPassword";
​
private PasswordEncoder passwordEncoder;
​
/**
* The password used to perform
* {@link PasswordEncoder#matches(CharSequence, String)} on when the user is
* not found to avoid SEC-2056. This is necessary, because some
* {@link PasswordEncoder} implementations will short circuit if the password is not
* in a valid format.
*/
private volatile String userNotFoundEncodedPassword;
​
private UserDetailsService userDetailsService;
​
private UserDetailsPasswordService userDetailsPasswordService;
​
public DaoAuthenticationProvider() {
setPasswordEncoder(PasswordEncoderFactories.createDelegatingPasswordEncoder());
}
​
@SuppressWarnings("deprecation")
protected void additionalAuthenticationChecks(UserDetails userDetails,
UsernamePasswordAuthenticationToken authentication)
throws AuthenticationException {

// 使用者未提交密碼，丟擲異常BadCredentialsException
if (authentication.getCredentials() == null) {
logger.debug("Authentication failed: no credentials provided");
​
throw new BadCredentialsException(messages.getMessage(
"AbstractUserDetailsAuthenticationProvider.badCredentials",
"Bad credentials"));
}

// 從傳入了Authentication物件中獲取使用者提交的密碼
String presentedPassword = authentication.getCredentials().toString();

// 用passwordEncoder的matches方法，比較使用者提交的密碼和userDetails中查詢到的正確密碼。
// 由於使用者密碼的存放一般都是hash後保密的，因此userDetails獲取到的密碼一般是一個hash值，而使用者提交
// 的是一個明文密碼，因此需要對使用者提交的密碼進行同樣的hash計算後再進行比較。
if (!passwordEncoder.matches(presentedPassword, userDetails.getPassword())) {
logger.debug("Authentication failed: password does not match stored value");
​
throw new BadCredentialsException(messages.getMessage(
"AbstractUserDetailsAuthenticationProvider.badCredentials",
"Bad credentials"));
}
}
​
protected void doAfterPropertiesSet() throws Exception {
Assert.notNull(this.userDetailsService, "A UserDetailsService must be set");
}
​
protected final UserDetails retrieveUser(String username,
UsernamePasswordAuthenticationToken authentication)
throws AuthenticationException {
prepareTimingAttackProtection();
try {
UserDetails loadedUser = this.getUserDetailsService().loadUserByUsername(username);
if (loadedUser == null) {
throw new InternalAuthenticationServiceException(
"UserDetailsService returned null, which is an interface contract violation");
}
return loadedUser;
}
catch (UsernameNotFoundException ex) {
mitigateAgainstTimingAttack(authentication);
throw ex;
}
catch (InternalAuthenticationServiceException ex) {
throw ex;
}
catch (Exception ex) {
throw new InternalAuthenticationServiceException(ex.getMessage(), ex);
}
}
​
@Override
protected Authentication createSuccessAuthentication(Object principal,
Authentication authentication, UserDetails user) {
boolean upgradeEncoding = this.userDetailsPasswordService != null
&& this.passwordEncoder.upgradeEncoding(user.getPassword());
if (upgradeEncoding) {
String presentedPassword = authentication.getCredentials().toString();
String newPassword = this.passwordEncoder.encode(presentedPassword);
user = this.userDetailsPasswordService.updatePassword(user, newPassword);
}
return super.createSuccessAuthentication(principal, authentication, user);
}
​
private void prepareTimingAttackProtection() {
if (this.userNotFoundEncodedPassword == null) {
this.userNotFoundEncodedPassword = this.passwordEncoder.encode(USER_NOT_FOUND_PASSWORD);
}
}
​
private void mitigateAgainstTimingAttack(UsernamePasswordAuthenticationToken authentication) {
if (authentication.getCredentials() != null) {
String presentedPassword = authentication.getCredentials().toString();
this.passwordEncoder.matches(presentedPassword, this.userNotFoundEncodedPassword);
}
}
​
/**
* Sets the PasswordEncoder instance to be used to encode and validate passwords. If
* not set, the password will be compared using {@link PasswordEncoderFactories#createDelegatingPasswordEncoder()}
*
* @param passwordEncoder must be an instance of one of the {@code PasswordEncoder}
* types.
*/
public void setPasswordEncoder(PasswordEncoder passwordEncoder) {
Assert.notNull(passwordEncoder, "passwordEncoder cannot be null");
this.passwordEncoder = passwordEncoder;
this.userNotFoundEncodedPassword = null;
}
​
protected PasswordEncoder getPasswordEncoder() {
return passwordEncoder;
}
​
public void setUserDetailsService(UserDetailsService userDetailsService) {
this.userDetailsService = userDetailsService;
}
​
protected UserDetailsService getUserDetailsService() {
return userDetailsService;
}
​
public void setUserDetailsPasswordService(
UserDetailsPasswordService userDetailsPasswordService) {
this.userDetailsPasswordService = userDetailsPasswordService;
}
}

AbstractUserDetailsAuthenticationProvider

可以看到 DaoAuthenticationProvider 繼承自 AbstractUserDetailsAuthenticationProvider , 而一個provider最核心的 authenticate 方法，便寫在了 AbstractUserDetailsAuthenticationProvider 中，下面我們只關注一下 authenticate 這個方法的原始碼。

public Authentication authenticate(Authentication authentication)
throws AuthenticationException {
Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,
() -> messages.getMessage(
"AbstractUserDetailsAuthenticationProvider.onlySupports",
"Only UsernamePasswordAuthenticationToken is supported"));
​
// 從傳入的Authentication物件中獲取使用者名稱
String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
: authentication.getName();

// 根據使用者名稱，從快取中獲取使用者的UserDetails
boolean cacheWasUsed = true;
UserDetails user = this.userCache.getUserFromCache(username);

if (user == null) {
cacheWasUsed = false;
// 如果從快取中沒有獲取到使用者，則通過方法retrieveUser來獲取使用者資訊
// retrieve方法為一個抽象方法，不同的子類中有不同的實現，而在子類中，一般又會通過UserDetailService來獲取使用者資訊，返回UserDetails
try {
user = retrieveUser(username,
(UsernamePasswordAuthenticationToken) authentication);
}
catch (UsernameNotFoundException notFound) {
logger.debug("User '" + username + "' not found");
​
if (hideUserNotFoundExceptions) {
throw new BadCredentialsException(messages.getMessage(
"AbstractUserDetailsAuthenticationProvider.badCredentials",
"Bad credentials"));
}
else {
throw notFound;
}
}
​
Assert.notNull(user,
"retrieveUser returned null - a violation of the interface contract");
}
​
try {
preAuthenticationChecks.check(user);
// additionalAuthenticationChecks為具體的認證邏輯，是一個抽象方法，在子類中實現。
// 比如前文中DaoAuthenticationProvider中，便是比較使用者提交的密碼和UserDetails中的密碼
additionalAuthenticationChecks(user,
(UsernamePasswordAuthenticationToken) authentication);
}
catch (AuthenticationException exception) {
if (cacheWasUsed) {
// There was a problem, so try again after checking
// we're using latest data (i.e. not from the cache)
cacheWasUsed = false;
user = retrieveUser(username,
(UsernamePasswordAuthenticationToken) authentication);
preAuthenticationChecks.check(user);
additionalAuthenticationChecks(user,
(UsernamePasswordAuthenticationToken) authentication);
}
else {
throw exception;
}
}
​
postAuthenticationChecks.check(user);
​
if (!cacheWasUsed) {
this.userCache.putUserInCache(user);
}
​
Object principalToReturn = user;
​
if (forcePrincipalAsString) {
principalToReturn = user.getUsername();
}
​
return createSuccessAuthentication(principalToReturn, authentication, user);
}

可以看到在 DaoAuthenticationProvider 中還用到 UserDetailsService 來查詢使用者的密碼許可權資訊，幷包裝為 UserDetails 返回，然後與使用者提交的使用者名稱密碼資訊進行比較來完成認證。 UserDetailsService 和 UserDetails 在不同的provider中都會被用到，關於這兩個介面的說明，在下一篇文章中介紹。

總結

最後我們總結一下這幾個介面和類

名稱	型別	說明
AuthenticationManager	介面	完成認證
ProviderManager	類	實現AuthenticationManager介面，將認證任務委託給不同的AuthenticationProvider
AuthenticationProvider	介面	具體認證邏輯的介面
AbstractUserDetailsAuthenticationProvider	抽象類	實現了AuthenticationProvider介面，獲取使用者資訊並完成認證的抽象類
DaoAuthenticationProvider	類	繼承AbstractUserDetailsAuthenticationProvider，實現具體的認證邏輯

這些類和介面之間的關係，大致可以用下圖進行表示