打開UsernamePasswordAuthenticationToken可得知，該實現類是Authentication的子類，因為Authentication是封裝了用戶的信息。
在該構造函數中，其中super(null)是調用了父類的方法
，
父類的方法如下：

    public AbstractAuthenticationToken(Collection<? extends GrantedAuthority> authorities) {
        if (authorities == null) { //為空時，需要賦個默認的權限，因為此時還未進行身份認證
            this.authorities = AuthorityUtils.NO_AUTHORITIES;   
            return;
        }

        for (GrantedAuthority a : authorities) {
            if (a == null) {
                throw new IllegalArgumentException(
                        "Authorities collection cannot contain any null elements");
            }
        }
        ArrayList<GrantedAuthority> temp = new ArrayList<GrantedAuthority>(
                authorities.size());
        temp.addAll(authorities);
        this.authorities = Collections.unmodifiableList(temp);
    }
 

setAuthenticated(false) 代表當前存進去的principal/credentials是否經過身份認證，此時肯定是沒有的。

setDetails(request, authRequest);

該方法會把請求的一些信息設置到UsernamePasswordAuthenticationToken裏面去，包括當前發起請求的IP，Session等

return this.getAuthenticationManager().authenticate(authRequest); //往AuthenticationManager靠攏

AuthenticationManager該類本身不包含校驗的邏輯，它的作用是用來管理AuthenticationProvider

public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
        Class<? extends Authentication> toTest = authentication.getClass();
        AuthenticationException lastException = null;
        Authentication result = null;
        boolean debug = logger.isDebugEnabled();

        for (AuthenticationProvider provider : getProviders()) { //
            if (!provider.supports(toTest)) {
                continue;
            }
            /*
            getProviders() 拿到所有的AuthenticationProvider，校驗邏輯都是在Provider中
            因為不同的登錄方式，它的認證邏輯是不通 的，目前使用的用戶名+密碼的方式，後續還會有第三方登錄，手機    號驗證碼登錄等，provider.supports(toTest)是否支持當前的登錄方式（判斷）
            對於用戶名密碼方式，它傳遞的token是：UsernamePasswordAuthenticationToken，而對於第三方登錄時的驗證方式則是SocialAuthenticationToken
            */

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

            try {
            //具體執行校驗邏輯
                result = provider.authenticate(authentication);

                if (result != null) {
                    copyDetails(authentication, result);
                    break;
                }
            }
            catch (AccountStatusException e) {
                prepareException(e, authentication);
                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 = parent.authenticate(authentication);
            }
            catch (ProviderNotFoundException e) {
            }
            catch (AuthenticationException e) {
                lastException = e;
            }
        }

        if (result != null) {
            if (eraseCredentialsAfterAuthentication
                    && (result instanceof CredentialsContainer)) {
                ((CredentialsContainer) result).eraseCredentials();
            }

            eventPublisher.publishAuthenticationSuccess(result);
            return result;
        }

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

        prepareException(lastException, authentication);

        throw lastException;
    }
 

provider.authenticate()實現類是寫在AuthenticationProvider的實現類AbstractUserDetailsAuthenticationProvider中

public Authentication authenticate(Authentication authentication)
            throws AuthenticationException {
        Assert.isInstanceOf(UsernamePasswordAuthenticationToken.class, authentication,
                messages.getMessage(
                        "AbstractUserDetailsAuthenticationProvider.onlySupports",
                        "Only UsernamePasswordAuthenticationToken is supported"));

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

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

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

            try {
            //獲取用戶信息，具體實現類在：DaoAuthenticationProvider.retrieveUser()
                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) {
                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);
    }

    protected final UserDetails retrieveUser(String username,
            UsernamePasswordAuthenticationToken authentication)
            throws AuthenticationException {
        UserDetails loadedUser;

        try {
            loadedUser = this.getUserDetailsService().loadUserByUsername(username);
            /**
            getUserDetailService在調用我們提供的UserDetailService的實現，也就是：MyUserDetailsService

            */
        }
        catch (UsernameNotFoundException notFound) {
            if (authentication.getCredentials() != null) {
                String presentedPassword = authentication.getCredentials().toString();
                passwordEncoder.isPasswordValid(userNotFoundEncodedPassword,
                        presentedPassword, null);
            }
            throw notFound;
        }
        catch (Exception repositoryProblem) {
            throw new InternalAuthenticationServiceException(
                    repositoryProblem.getMessage(), repositoryProblem);
        }

        if (loadedUser == null) {
            throw new InternalAuthenticationServiceException(
                    "UserDetailsService returned null, which is an interface contract violation");
        }
        return loadedUser;
    }

拿到用戶信息之後，回到AbstractUserDetailsAuthenticationProvider

try {
            preAuthenticationChecks.check(user);
            additionalAuthenticationChecks(user,
                    (UsernamePasswordAuthenticationToken) authentication);
                    //在dao裏校驗密碼是否匹配
        }

它會預檢查用戶是否過期，是否禁用，之後檢查密碼是否匹配。
預檢查之後還會有後置檢查

postAuthenticationChecks.check(user);  //

所有檢查都通過，就會認為用戶的認證是成功的。

return createSuccessAuthentication(principalToReturn, authentication, user);

protected Authentication createSuccessAuthentication(Object principal,
            Authentication authentication, UserDetails user) {
        UsernamePasswordAuthenticationToken result = new UsernamePasswordAuthenticationToken(
                principal, authentication.getCredentials(),
                authoritiesMapper.mapAuthorities(user.getAuthorities()));
        result.setDetails(authentication.getDetails());

        return result;
    }

再次new 了UsernamePasswordAuthenticationToken對象，區別再與構造方法不同，傳遞的參數不同，這個時候權限，用戶信息都已經拿到

2.認證結果如何在多個請求之間共享

3.獲取用戶認證的信息

串理spring security認證流程源碼