springsecurity 源码解读 之 RememberMeAuthenticationFilter

RememberMeAuthenticationFilter 的作用很简单，就是用于当session 过期后，系统自动通过读取cookie 让系统自动登录。

我们来看看Springsecurity的过滤器链条。

我们发现这个 RememberMeAuthenticationFilter  在 匿名构造器之前，这个是为什么呢？

还是从源码来分析：

if (SecurityContextHolder.getContext().getAuthentication() == null) {
            Authentication rememberMeAuth = rememberMeServices.autoLogin(request, response);

            if (rememberMeAuth != null) {

代码中有这样的一行，当SecurityContext 中 Authentication 为空时，他就会调用 rememberMeServices 自动登录。

因此刚刚的问题也就好解释了，因为如果RememberMeAuthenticationFilter  没有实现自动登录，那么他的Authentication 还是为空，

这是可以创建一个匿名登录，如果先创建了匿名登录，那么这个 RememberMeAuthenticationFilter   的判断就不会为null，过滤器将失效。

我们看看rememberMeServices 的autoLogin 登录

我们贴出实现的代码：

public final Authentication autoLogin(HttpServletRequest request, HttpServletResponse response) {
        String rememberMeCookie = extractRememberMeCookie(request);

        if (rememberMeCookie == null) {
            return null;
        }

        logger.debug("Remember-me cookie detected");

        if (rememberMeCookie.length() == 0) {
            logger.debug("Cookie was empty");
            cancelCookie(request, response);
            return null;
        }

        UserDetails user = null;

        try {
            String[] cookieTokens = decodeCookie(rememberMeCookie);
            user = processAutoLoginCookie(cookieTokens, request, response);
            userDetailsChecker.check(user);

            logger.debug("Remember-me cookie accepted");

            return createSuccessfulAuthentication(request, user);
        } catch (CookieTheftException cte) {
            cancelCookie(request, response);
            throw cte;
        } catch (UsernameNotFoundException noUser) {
            logger.debug("Remember-me login was valid but corresponding user not found.", noUser);
        } catch (InvalidCookieException invalidCookie) {
            logger.debug("Invalid remember-me cookie: " + invalidCookie.getMessage());
        } catch (AccountStatusException statusInvalid) {
            logger.debug("Invalid UserDetails: " + statusInvalid.getMessage());
        } catch (RememberMeAuthenticationException e) {
            logger.debug(e.getMessage());
        }

        cancelCookie(request, response);
        return null;
    }

extractRememberMeCookie这个方法判断 SPRING_SECURITY_REMEMBER_ME_COOKIE 这样的cookie，如果没有就直接返回了null。

processAutoLoginCookie：这个是处理cookie 并从cookie加载用户。

默认springsecurity 使用类 TokenBasedRememberMeServices 来解析 cookie。

实现代码如下：

protected UserDetails processAutoLoginCookie(String[] cookieTokens, HttpServletRequest request,
            HttpServletResponse response) {

        if (cookieTokens.length != 3) {
            throw new InvalidCookieException("Cookie token did not contain 3" +
                    " tokens, but contained '" + Arrays.asList(cookieTokens) + "'");
        }

        long tokenExpiryTime;

        try {
            tokenExpiryTime = new Long(cookieTokens[1]).longValue();
        }
        catch (NumberFormatException nfe) {
            throw new InvalidCookieException("Cookie token[1] did not contain a valid number (contained '" +
                    cookieTokens[1] + "')");
        }

        if (isTokenExpired(tokenExpiryTime)) {
            throw new InvalidCookieException("Cookie token[1] has expired (expired on '"
                    + new Date(tokenExpiryTime) + "'; current time is '" + new Date() + "')");
        }

        // Check the user exists.
        // Defer lookup until after expiry time checked, to possibly avoid expensive database call.

        UserDetails userDetails = getUserDetailsService().loadUserByUsername(cookieTokens[0]);

        // Check signature of token matches remaining details.
        // Must do this after user lookup, as we need the DAO-derived password.
        // If efficiency was a major issue, just add in a UserCache implementation,
        // but recall that this method is usually only called once per HttpSession - if the token is valid,
        // it will cause SecurityContextHolder population, whilst if invalid, will cause the cookie to be cancelled.
        String expectedTokenSignature = makeTokenSignature(tokenExpiryTime, userDetails.getUsername(),
                userDetails.getPassword());

        if (!equals(expectedTokenSignature,cookieTokens[2])) {
            throw new InvalidCookieException("Cookie token[2] contained signature '" + cookieTokens[2]
                                                                                                    + "' but expected '" + expectedTokenSignature + "'");
        }

        return userDetails;
    }

　　

 protected String makeTokenSignature(long tokenExpiryTime, String username, String password) {
        String data = username + ":" + tokenExpiryTime + ":" + password + ":" + getKey();
        MessageDigest digest;
        try {
            digest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException("No MD5 algorithm available!");
        }

        return new String(Hex.encode(digest.digest(data.getBytes())));
    }

这个代码就是加载用户，并验证cookie 是否有效。

因此我们在写入cookie 时，产生的cookie 过程如下：

String enPassword=EncryptUtil.hexToBase64(password);
        
        long tokenValiditySeconds = 1209600; // 14 days
        long tokenExpiryTime = System.currentTimeMillis() + (tokenValiditySeconds * 1000);
        String signatureValue = makeTokenSignature(tokenExpiryTime,username,enPassword);
        String tokenValue = username + ":" + tokenExpiryTime + ":" + signatureValue;
        String tokenValueBase64 = new String(Base64.encodeBase64(tokenValue.getBytes()));
                
        CookieUtil.addCookie(TokenBasedRememberMeServices.SPRING_SECURITY_REMEMBER_ME_COOKIE_KEY, 
                tokenValueBase64,60 * 60 * 24 * 365, true, request, response);