public interface AuthenticationProvider {
	// 具體認(rèn)證流程
	Authentication authenticate(Authentication authentication)
			throws AuthenticationException;	
    // supports函數(shù)用來(lái)指明該P(yáng)rovider是否適用于該類(lèi)型的認(rèn)證，如果不合適，則尋找另一個(gè)Provider進(jìn)行驗(yàn)證處理。	
	boolean supports(Class<?> authentication);
}

 @Override
    protected void configure(AuthenticationManagerBuilder auth) {
        auth.authenticationProvider(authenticationProvider());
    }

public interface AuthenticationManager {
	Authentication authenticate(Authentication authentication)
			throws AuthenticationException;
}

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();

		for (AuthenticationProvider provider : getProviders()) {
			// 如果支持認(rèn)證實(shí)現(xiàn)類(lèi)就繼續(xù)處理
			if (!provider.supports(toTest)) {
				continue;
			}

			if (debug) {
				logger.debug("Authentication attempt using "
						+ provider.getClass().getName());
			}

			try {
			  // 調(diào)用實(shí)現(xiàn)類(lèi)的authenticate方法進(jìn)行真實(shí)業(yè)務(wù)邏輯認(rèn)證處理
				result = provider.authenticate(authentication);

				if (result != null) {
					copyDetails(authentication, result);
					break;
				}
			}
			catch (AccountStatusException e) {
				prepareException(e, authentication);
				// SEC-546: Avoid polling additional providers if auth failure is due to
				// invalid account status
				throw e;
			}
			catch (InternalAuthenticationServiceException e) {
				prepareException(e, authentication);
				throw e;
			}
			catch (AuthenticationException e) {
				lastException = e;
			}
		}

		if (result == null && parent != null) {
			// Allow the parent to try.
			try {
				result = parentResult = parent.authenticate(authentication);
			}
			catch (ProviderNotFoundException e) {
				// ignore as we will throw below if no other exception occurred prior to
				// calling parent and the parent
				// may throw ProviderNotFound even though a provider in the child already
				// handled the request
			}
			catch (AuthenticationException e) {
				lastException = parentException = e;
			}
		}

		if (result != null) {
			if (eraseCredentialsAfterAuthentication
					&& (result instanceof CredentialsContainer)) {
				// Authentication is complete. Remove credentials and other secret data
				// from authentication
				((CredentialsContainer) result).eraseCredentials();
			}

			// If the parent AuthenticationManager was attempted and successful than it will publish an AuthenticationSuccessEvent
			// This check prevents a duplicate AuthenticationSuccessEvent if the parent AuthenticationManager already published it
			if (parentResult == null) {
			  //  //發(fā)送認(rèn)證成功事件
				eventPublisher.publishAuthenticationSuccess(result);
			}
			return result;
		}

		// Parent was null, or didn't authenticate (or throw an exception).

		if (lastException == null) {
			lastException = new ProviderNotFoundException(messages.getMessage(
					"ProviderManager.providerNotFound",
					new Object[] { toTest.getName() },
					"No AuthenticationProvider found for {0}"));
		}

		// If the parent AuthenticationManager was attempted and failed than it will publish an AbstractAuthenticationFailureEvent
		// This check prevents a duplicate AbstractAuthenticationFailureEvent if the parent AuthenticationManager already published it
		if (parentException == null) {
			prepareException(lastException, authentication);
		}

		throw lastException;
	}