Well, at least if you want to run multiple instances of your application. And, additionally, it’s not necessary, at least in most cases. There’s another mechanism for keeping some user session state in a web application. It’s called Cookie. And, instead of using it only to store a session identifier, why not let it hold the data itself. This blog post shows, that, with some effort, it’s possible to configure Spring Security to store its session information in a cookie instead of a server-side session.

Spring Security architecture

Spring Security integrates into Spring web as a servlet request filter (see Chapter 9 of the Spring Security Reference). The FilterChainProxy is the central filter class and contains a parallel SecurityFilterChain (see Chapter 9.4 of the Spring Security Reference). The FilterChainProxy is also a good starting point for debugging the Spring Security processing.

In our sample project (using Spring Boot 2.3.1 and Spring Security 5.3.3) the SecurityFilterChain contains the following filters (identified by debugging into FilterChainProxy.doFilter(...) and looking into this.filterChains[0].filters).

Let’s have a closer look at those filters that are relevant for our purpose and how to extend and customize their behaviour.

SecurityContextPersistenceFilter

From the API documentation: «Populates the SecurityContextHolder with information obtained from the configured SecurityContextRepository prior to the request and stores it back in the repository once the request has completed and clearing the context holder.»

The SecurityContext mainly represents the persisted session. It contains an Authentication which in the context of a web application encapsulates the information of the authenticated user. The default implementation of the SecurityContextRepository stores the SecurityContext in the HttpSession. To change this behaviour we have to provide our own SecurityContextRepository implementation.

@Component
public class CookieSecurityContextRepository implements SecurityContextRepository {

  private static final String EMPTY_CREDENTIALS = "";
  private static final String ANONYMOUS_USER = "anonymousUser";

  private final String cookieHmacKey;

  public CookieSecurityContextRepository(@Value("${auth.cookie.hmac-key}") String cookieHmacKey) {
    this.cookieHmacKey = cookieHmacKey;
  }

  @Override
  public SecurityContext loadContext(HttpRequestResponseHolder requestResponseHolder) {
    HttpServletRequest request = requestResponseHolder.getRequest();
    HttpServletResponse response = requestResponseHolder.getResponse();
    requestResponseHolder.setResponse(new SaveToCookieResponseWrapper(request, response));

    SecurityContext context = SecurityContextHolder.createEmptyContext();
    readUserInfoFromCookie(request).ifPresent(userInfo ->
      context.setAuthentication(new UsernamePasswordAuthenticationToken(userInfo, EMPTY_CREDENTIALS, userInfo.getAuthorities())));

    return context;
  }

  @Override
  public void saveContext(SecurityContext context, HttpServletRequest request, HttpServletResponse response) {
    SaveToCookieResponseWrapper responseWrapper = (SaveToCookieResponseWrapper) response;
    if (!responseWrapper.isContextSaved()) {
      responseWrapper.saveContext(context);
    }
  }

  @Override
  public boolean containsContext(HttpServletRequest request) {
    return readUserInfoFromCookie(request).isPresent();
  }

  private Optional<UserInfo> readUserInfoFromCookie(HttpServletRequest request) {
    return readCookieFromRequest(request)
      .map(this::createUserInfo);
  }

  private Optional<Cookie> readCookieFromRequest(HttpServletRequest request) {
    if (request.getCookies() == null) {
      return Optional.empty();
    }

    Optional<Cookie> maybeCookie = Stream.of(request.getCookies())
      .filter(c -> SignedUserInfoCookie.NAME.equals(c.getName()))
      .findFirst();

    return maybeCookie;
  }

  private UserInfo createUserInfo(Cookie cookie) {
    return new SignedUserInfoCookie(cookie, cookieHmacKey).getUserInfo();
  }

  private class SaveToCookieResponseWrapper extends SaveContextOnUpdateOrErrorResponseWrapper {
    private final HttpServletRequest request;

    SaveToCookieResponseWrapper(HttpServletRequest request, HttpServletResponse response) {
      super(response, true);
      this.request = request;
    }

    @Override
    protected void saveContext(SecurityContext securityContext) {
      HttpServletResponse response = (HttpServletResponse) getResponse();
      Authentication authentication = securityContext.getAuthentication();

      // some checks, see full sample code


      UserInfo userInfo = (UserInfo) authentication.getPrincipal();
      SignedUserInfoCookie cookie = new SignedUserInfoCookie(userInfo, cookieHmacKey);
      cookie.setSecure(request.isSecure());
      response.addCookie(cookie);
    }
  }
}

The UserInfo in our sample project is a very simple POJO that implements the UserDetails interface and contains the information that we want to hold in our user session.

The SaveToCookieResponseWrapper gets the UserInfo from the SecurityContext and puts it into a SignedUserInfoCookie. The SignedUserInfoCookie is an extension of javax.servlet.http.Cookie that handles the serialization and deserialization of the UserInfo into/from the cookie value.

public class SignedUserInfoCookie extends Cookie {

  public static final String NAME = "UserInfo";
  private static final String PATH = "/";
  private static final Pattern UID_PATTERN = Pattern.compile("uid=([A-Za-z0-9]*)");
  private static final Pattern ROLES_PATTERN = Pattern.compile("roles=([A-Z0-9_|]*)");
  private static final Pattern COLOUR_PATTERN = Pattern.compile("colour=([A-Z]*)");
  private static final Pattern HMAC_PATTERN = Pattern.compile("hmac=([A-Za-z0-9+/=]*)");
  private static final String HMAC_SHA_512 = "HmacSHA512";

  private final Payload payload;
  private final String hmac;

  public SignedUserInfoCookie(UserInfo userInfo, String cookieHmacKey) {
    super(NAME, "");
    this.payload = new Payload(
      userInfo.getUsername(),
      userInfo.getAuthorities().stream().map(GrantedAuthority::getAuthority).collect(toList()),
      userInfo.getColour().orElse(null));
    this.hmac = calculateHmac(this.payload, cookieHmacKey);
    this.setPath(PATH);
    this.setMaxAge((int) Duration.of(1, ChronoUnit.HOURS).toSeconds());
    this.setHttpOnly(true);
  }

  public SignedUserInfoCookie(Cookie cookie, String cookieHmacKey) {
    super(NAME, "");

    if (!NAME.equals(cookie.getName()))
      throw new IllegalArgumentException("No " + NAME + " Cookie");

    this.hmac = parse(cookie.getValue(), HMAC_PATTERN).orElse(null);
    if (hmac == null)
      throw new CookieVerificationFailedException("Cookie not signed (no HMAC)");

    String username = parse(cookie.getValue(), UID_PATTERN).orElseThrow(() -> new IllegalArgumentException(NAME + " Cookie contains no UID"));
    List<String> roles = parse(cookie.getValue(), ROLES_PATTERN).map(s -> List.of(s.split("\\|"))).orElse(List.of());
    String colour = parse(cookie.getValue(), COLOUR_PATTERN).orElse(null);
    this.payload = new Payload(username, roles, colour);

    if (!hmac.equals(calculateHmac(payload, cookieHmacKey)))
      throw new CookieVerificationFailedException("Cookie signature (HMAC) invalid");

    this.setPath(cookie.getPath());
    this.setMaxAge(cookie.getMaxAge());
    this.setHttpOnly(cookie.isHttpOnly());
  }

  private static Optional<String> parse(String value, Pattern pattern) {
    Matcher matcher = pattern.matcher(value);
    if (!matcher.find())
      return Optional.empty();

    if (matcher.groupCount() < 1)
      return Optional.empty();

    String match = matcher.group(1);
    if (match == null || match.trim().isEmpty())
      return Optional.empty();

    return Optional.of(match);
  }

  @Override
  public String getValue() {
    return payload.toString() + "&hmac=" + hmac;
  }

  public UserInfo getUserInfo() {
    return new UserInfo(
      payload.username,
      payload.roles.stream().map(SimpleGrantedAuthority::new).collect(Collectors.toSet()),
      payload.colour);
  }

  private String calculateHmac(Payload payload, String secretKey) {
    byte[] secretKeyBytes = Objects.requireNonNull(secretKey).getBytes(StandardCharsets.UTF_8);
    byte[] valueBytes = Objects.requireNonNull(payload).toString().getBytes(StandardCharsets.UTF_8);

    try {
      Mac mac = Mac.getInstance(HMAC_SHA_512);
      SecretKeySpec secretKeySpec = new SecretKeySpec(secretKeyBytes, HMAC_SHA_512);
      mac.init(secretKeySpec);
      byte[] hmacBytes = mac.doFinal(valueBytes);
      return Base64.getEncoder().encodeToString(hmacBytes);

    } catch (NoSuchAlgorithmException | InvalidKeyException e) {
      throw new RuntimeException(e);
    }
  }

  private static class Payload {
    private final String username;
    private final List<String> roles;
    private final String colour;

    private Payload(String username, List<String> roles, String colour) {
      this.username = username;
      this.roles = roles;
      this.colour = colour;
    }

    @Override
    public String toString() {
      return "uid=" + username +
        "&roles=" + String.join("|", roles) +
        (colour != null ? "&colour=" + colour : "");
    }
  }
}

The cookie value has to follow RFC-6265 which allows only a few non-alphabetical characters (see Stack Overflow answer for a good summary), for example no whitespace, quotes or brackets are allowed. So we can’t use a JSON structure to serialize our payload, which would probably be easier to handle, especially to parse. We could have encoded the payload with Base64 before writing it into the cookie. However, the idea of the sample project was to keep the cookie value unencoded and human-readable, so we decided for the individual format.

As the cookie contains the id and the roles of the authenticated user, we have to make sure that the value is not modified on the client side. To do this our sample application signs the cookie by computing a HMAC (hash-based message authentication code) of the payload and appending it to the cookie value. That’s a quite simple approach and there are probably better and more secure ways of securing the cookie. One option might be JWT which provides a standardized way to securely exchange sensitive data. But, this is a topic of its own and out of the scope of this blog post.

(Thanks to Christian Köberl, @derkoe, for his feedback and ideas to improve the security of the cookie)

When the SecurityContext is requested via SecurityContextRepository.loadContext(...), the javax.servlet.http.Cookie from the HttpServletRequest is transformed into a SignedUserInfoCookie again. The cookie value is verified using the HMAC signature. A CookieVerificationFailedException will be thrown if the received cookie is unsigned or the HMAC does not fit to the value. Finally, the UserInfo is retrieved from the SignedUserInfoCookie, wrapped in a UsernamePasswordAuthenticationToken and set into the SecurityContext.

UsernamePasswordAuthenticationFilter

From the API documentation: «Processes an authentication form submission.»

See also Chapter 10 of the Spring Security Reference for a detailed description of the Spring Security authentication process.

The UsernamePasswordAuthenticationFilter triggers the authentication, if necessary and possible. It reads username and password from a login form request, wraps them into a UsernamePasswordAuthenticationToken and calls the configured AuthenticationManager to perform the authentication.

In the default configuration, the AuthenticationManager is a ProviderManager which holds a list of AuthenticationProviders to which it delegates the authentication request. In our sample project we use a very basic InMemoryAuthenticationProvider which knows only one static user. In a real world project we would instead use a database or LDAP provider (from the Spring Security LDAP module).

After a successful login the configured AuthenticationSuccessHandler is called. Usually, this handler decides about where to forward the user to after the successful login. In the default configuration a SavedRequestAwareAuthenticationSuccessHandler is used. It loads and replays the original request (which was cached before by the ExceptionTranslationFilter, see next section) to show the page to the user which he/she originally requested. As this RequestCache is also stored in the server-side session, we have to find another strategy for this feature as well.

@Component
public class RedirectToOriginalUrlAuthenticationSuccessHandler extends SimpleUrlAuthenticationSuccessHandler {
  private static final String DEFAULT_TARGET_URL = "/";

  public RedirectToOriginalUrlAuthenticationSuccessHandler() {
    super(DEFAULT_TARGET_URL);
    this.setTargetUrlParameter(WebSecurityConfig.TARGET_AFTER_SUCCESSFUL_LOGIN_PARAM);
  }

  @Override
  public void onAuthenticationSuccess(HttpServletRequest request, HttpServletResponse response, Authentication authentication) throws IOException, ServletException {
    UserInfo userInfo = (UserInfo) authentication.getPrincipal();
    userInfo.setColour(request.getParameter(WebSecurityConfig.COLOUR_PARAM));
    super.onAuthenticationSuccess(request, response, authentication);
  }

  @Override
  protected String determineTargetUrl(HttpServletRequest request, HttpServletResponse response, Authentication authentication) {
    var targetUrl = super.determineTargetUrl(request, response, authentication);
    if (UrlUtils.isAbsoluteUrl(targetUrl)) {
      LOG.warn("Absolute target URL {} identified and suppressed", targetUrl);
      return DEFAULT_TARGET_URL;
    }
    return targetUrl;
  }
}

The RedirectToOriginalUrlAuthenticationSuccessHandler extends the SimpleUrlAuthenticationSuccessHandler and sets the targetUrlParameter in its constructor. The parameter is defined and used by the extended AbstractAuthenticationTargetUrlRequestHandler to find the target URL in the request parameters. Using this feature, we can simply put the originally requested URL into a hidden input field of the login form. The determineTargetUrl(...) method of the AbstractAuthenticationTargetUrlRequestHandler is overridden to prevent tampering of the target URL parameter (see OWASP Unvalidated Redirects and Forwards Cheat Sheet). We only expect relative URLs within our own application.

The RedirectToOriginalUrlAuthenticationSuccessHandler also overrides the onAuthenticationSuccess(...) method. In this method we can get additional parameters (in our example a favorite colour) from the login form and add it to the UserInfo object.

ExceptionTranslationFilter

From the API documentation: «Handles any AccessDeniedException and AuthenticationException thrown within the filter chain.»

Especially the very first, unauthorized request of a user triggers an AccessDeniedException (somewhere out of the FilterSecurityInterceptor). This one is catched and handled by the ExceptionTranslationFilter. If the user is not yet authenticated, the filter forwards him/her to the configured AuthenticationEntryPoint.

In the default configuration, the original request is temporarily stored in a RequestCache to be replayed after a successful login (see previous section). As noted before, the default HttpSessionRequestCache also uses the server session to store the request. We could have introduced a CookieRequestCache to stored the request in another cookie (like the SecurityContext). In our sample project we follow another approach.

We deactivate the RequestCache and instead extend the default LoginUrlAuthenticationEntryPoint, which forwards the user to the login form.

@Component
public class LoginWithTargetUrlAuthenticationEntryPoint extends LoginUrlAuthenticationEntryPoint {

  public LoginWithTargetUrlAuthenticationEntryPoint() {
    super(WebSecurityConfig.LOGIN_FORM_URL);
  }

  @Override
  protected String determineUrlToUseForThisRequest(HttpServletRequest request, HttpServletResponse response, AuthenticationException exception) {
    return UriComponentsBuilder.fromUriString(super.determineUrlToUseForThisRequest(request, response, exception))
      .queryParam(WebSecurityConfig.TARGET_AFTER_SUCCESSFUL_LOGIN_PARAM, request.getRequestURI())
      .toUriString();
  }
}

The overridden determineUrlToUseForThisRequest(...) method appends the URL from the original request as a query parameter to the redirect URL. This way, the URL can be mapped to a hidden input field and will be included again in the login request where the AuthenticationSuccessHandler can read it (see previous section).

WebSecurityConfig

The WebSecurityConfig configures Spring Security to use all the components described above.

@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

  static final String LOGIN_FORM_URL = "/login";
  static final String TARGET_AFTER_SUCCESSFUL_LOGIN_PARAM = "target";
  static final String COLOUR_PARAM = "colour";

  private final CookieSecurityContextRepository cookieSecurityContextRepository;
  private final LoginWithTargetUrlAuthenticationEntryPoint loginWithTargetUrlAuthenticationEntryPoint;
  private final RedirectToOriginalUrlAuthenticationSuccessHandler redirectToOriginalUrlAuthenticationSuccessHandler;
  private final InMemoryAuthenticationProvider inMemoryAuthenticationProvider;

  protected WebSecurityConfig(CookieSecurityContextRepository cookieSecurityContextRepository,
                              LoginWithTargetUrlAuthenticationEntryPoint loginWithTargetUrlAuthenticationEntryPoint,
                              RedirectToOriginalUrlAuthenticationSuccessHandler redirectToOriginalUrlAuthenticationSuccessHandler,
                              InMemoryAuthenticationProvider inMemoryAuthenticationProvider) {
    super();
    this.cookieSecurityContextRepository = cookieSecurityContextRepository;
    this.loginWithTargetUrlAuthenticationEntryPoint = loginWithTargetUrlAuthenticationEntryPoint;
    this.redirectToOriginalUrlAuthenticationSuccessHandler = redirectToOriginalUrlAuthenticationSuccessHandler;
    this.inMemoryAuthenticationProvider = inMemoryAuthenticationProvider;
  }

  @Override
  protected void configure(HttpSecurity http) throws Exception {
    http
      // deactivate session creation

      .sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS)
      .and().csrf().disable()

      // store SecurityContext in Cookie / delete Cookie on logout

      .securityContext().securityContextRepository(cookieSecurityContextRepository)
      .and().logout().permitAll().deleteCookies(SignedUserInfoCookie.NAME)

      // deactivate RequestCache and append originally requested URL as query parameter to login form request

      .and().requestCache().disable()
      .exceptionHandling().authenticationEntryPoint(loginWithTargetUrlAuthenticationEntryPoint)

      // configure form-based login

      .and().formLogin()
      .loginPage(LOGIN_FORM_URL)
      // after successful login forward user to originally requested URL

      .successHandler(redirectToOriginalUrlAuthenticationSuccessHandler)

      .and().authorizeRequests()
      .antMatchers(LOGIN_FORM_URL).permitAll()
      .antMatchers("/**").authenticated();
  }

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

}

To prevent the creation of the server-side session and the JSESSION cookie we use the SessionCreationPolicy.STATELESS. To really activate this policy, we have to disable CSRF protection as well (see Spring Security issue 5299).

We use the CookieSecurityContextRepository and our cookie should be deleted after the user logs out.

The RequestCache is deactivated and instead the LoginWithTargetUrlAuthenticationEntryPoint is used to add the originally requested URL to the login form request.

The RedirectToOriginalUrlAuthenticationSuccessHandler is used to forward the user to the originally requested URL after a successful login.

Summary

Spring Security might seem to be very complex and hard to configure on the first glance. But, spending some time with the documentation and doing a little bit of debugging in a sample application, it turns out that it is very extensible and customizable by design. The hardest part is to find the right places. This blog post identified the ones that need to be adjusted to store the user session information in a cookie instead of a server-side session. It might also be a starting point for other, related topics.

Many thanks to Michael Vitz for showing me the relevant starting points and reviewing the resulting implementation. Also many thanks to Jochen Christ, Jan Stępień, and Stefan Tilkov for their feedback to this post.

Header Photo by Steve Halama on Unsplash

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