public interface AuthenticationManager {
	/**
	* 定义的一个认证的方法
	**/
	Authentication authenticate(Authentication authentication)
			throws AuthenticationException;
}

public class ProviderManager implements AuthenticationManager, MessageSourceAware,
		InitializingBean {
	// 多种认证方式
	private List<AuthenticationProvider> providers = Collections.emptyList();

	private AuthenticationManager parent;
	private boolean eraseCredentialsAfterAuthentication = true;

	/**
	 * 遍历每一种认证方式，进行认证
	 **/
	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();
		// 遍历每一种认证方式
		for (AuthenticationProvider provider : getProviders()) {
			if (!provider.supports(toTest)) {
				continue;
			}
			// 忽略...
			try {
				// 调用具体的认证方法
				result = provider.authenticate(authentication);

				if (result != null) {
					copyDetails(authentication, result);
					break;
				}
			}
			catch (AccountStatusException | InternalAuthenticationServiceException e) {
				prepareException(e, authentication);
				throw e;
			} catch (AuthenticationException e) {
				lastException = e;
			}
		}
		// 忽略...
	}
}

public interface AuthenticationProvider {
	/**
	 * 认证逻辑实现的方法
	 */
	Authentication authenticate(Authentication authentication)
			throws AuthenticationException;

	/**
	 * 判断当前provider是否支持该Authentication
	 * /
	boolean supports(Class<?> authentication);
}

public abstract class AbstractUserDetailsAuthenticationProvider implements
		AuthenticationProvider, InitializingBean, MessageSourceAware {
	// 抽象定义
	protected abstract void additionalAuthenticationChecks(UserDetails userDetails,
			UsernamePasswordAuthenticationToken authentication)
			throws AuthenticationException;

	// 定义主要流程，关键账号验证和密码验证在具体实现类中实现
	public Authentication authenticate(Authentication authentication)
			throws AuthenticationException {
		Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,
				() -> messages.getMessage(
						"AbstractUserDetailsAuthenticationProvider.onlySupports",
						"Only UsernamePasswordAuthenticationToken is supported"));

		// Determine username
		String username = (authentication.getPrincipal() == null) ? "NONE_PROVIDED"
				: authentication.getName();

		boolean cacheWasUsed = true;
		UserDetails user = this.userCache.getUserFromCache(username);

		if (user == null) {
			cacheWasUsed = false;

			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(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);
	}

	
		UsernamePasswordAuthenticationToken result = new UsernamePasswordAuthenticationToken(
				principal, authentication.getCredentials(),
				authoritiesMapper.mapAuthorities(user.getAuthorities()));
		result.setDetails(authentication.getDetails());

		return result;
	}
	// 抽象的 账号验证
	protected abstract UserDetails retrieveUser(String username,
			UsernamePasswordAuthenticationToken authentication)
			throws AuthenticationException;

	public boolean supports(Class<?> authentication) {
		return (UsernamePasswordAuthenticationToken.class
				.isAssignableFrom(authentication));
	}

}

	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);
		}
	}
	@SuppressWarnings("deprecation")
	protected void additionalAuthenticationChecks(UserDetails userDetails,
			UsernamePasswordAuthenticationToken authentication)
			throws AuthenticationException {
		if (authentication.getCredentials() == null) {
			logger.debug("Authentication failed: no credentials provided");

			throw new BadCredentialsException(messages.getMessage(
					"AbstractUserDetailsAuthenticationProvider.badCredentials",
					"Bad credentials"));
		}

		String presentedPassword = authentication.getCredentials().toString();

		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"));
		}
	}