Two factor authentication with spring security oauth2

Question

I'm looking for ideas how to implement two factor authentication (2FA) with spring security OAuth2. The requirement is that the user needs two factor authentication only for specific applications with sensitive information. Those webapps have their own client ids.

One idea that popped in my mind would be to "mis-use" the scope approval page to force the user to enter the 2FA code/PIN (or whatever).

Sample flows would look like this:

Accessing apps without and with 2FA

• User is logged out
• User accesses app A which does not require 2FA
• Redirect to OAuth app, user logs in with username and password
• Redirected back to app A and user is logged in
• User accesses app B which also does not require 2FA
• Redirect to OAuth app, redirect back to app B and user is directly logged in
• User accesses app S which does require 2FA
• Redirect to OAuth app, user needs to additionally provide the 2FA token
• Redirected back to app S and user is logged in

Directly accessing app with 2FA

• User is logged out
• User accesses app S which does require 2FA
• Redirect to OAuth app, user logs in with username and password, user needs to additionally provide the 2FA token
• Redirected back to app S and user is logged in

Do you have other ideas how to apporach this?

Answer 1

So this is how two factor authentication has been implemented finally:

A filter is registered for the /oauth/authorize path after the spring security filter:

@Order(200)
public class SecurityWebApplicationInitializer extends AbstractSecurityWebApplicationInitializer {
    @Override
    protected void afterSpringSecurityFilterChain(ServletContext servletContext) {
        FilterRegistration.Dynamic twoFactorAuthenticationFilter = servletContext.addFilter("twoFactorAuthenticationFilter", new DelegatingFilterProxy(AppConfig.TWO_FACTOR_AUTHENTICATION_BEAN));
        twoFactorAuthenticationFilter.addMappingForUrlPatterns(null, false, "/oauth/authorize");
        super.afterSpringSecurityFilterChain(servletContext);
    }
}

This filter checks if the user hasn't already authenticated with a 2nd factor (by checking if the ROLE_TWO_FACTOR_AUTHENTICATED authority isn't available) and creates an OAuth AuthorizationRequest which is put into the session. The user is then redirected to the page where he has to enter the 2FA code:

/**
 * Stores the oauth authorizationRequest in the session so that it can
 * later be picked by the {@link com.example.CustomOAuth2RequestFactory}
 * to continue with the authoriztion flow.
 */
public class TwoFactorAuthenticationFilter extends OncePerRequestFilter {

    private RedirectStrategy redirectStrategy = new DefaultRedirectStrategy();

    private OAuth2RequestFactory oAuth2RequestFactory;

    @Autowired
    public void setClientDetailsService(ClientDetailsService clientDetailsService) {
        oAuth2RequestFactory = new DefaultOAuth2RequestFactory(clientDetailsService);
    }

    private boolean twoFactorAuthenticationEnabled(Collection<? extends GrantedAuthority> authorities) {
        return authorities.stream().anyMatch(
            authority -> ROLE_TWO_FACTOR_AUTHENTICATION_ENABLED.equals(authority.getAuthority())
        );
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {
        // Check if the user hasn't done the two factor authentication.
        if (AuthenticationUtil.isAuthenticated() && !AuthenticationUtil.hasAuthority(ROLE_TWO_FACTOR_AUTHENTICATED)) {
            AuthorizationRequest authorizationRequest = oAuth2RequestFactory.createAuthorizationRequest(paramsFromRequest(request));
            /* Check if the client's authorities (authorizationRequest.getAuthorities()) or the user's ones
               require two factor authenticatoin. */
            if (twoFactorAuthenticationEnabled(authorizationRequest.getAuthorities()) ||
                    twoFactorAuthenticationEnabled(SecurityContextHolder.getContext().getAuthentication().getAuthorities())) {
                // Save the authorizationRequest in the session. This allows the CustomOAuth2RequestFactory
                // to return this saved request to the AuthenticationEndpoint after the user successfully
                // did the two factor authentication.
                request.getSession().setAttribute(CustomOAuth2RequestFactory.SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME, authorizationRequest);

                // redirect the the page where the user needs to enter the two factor authentiation code
                redirectStrategy.sendRedirect(request, response,
                        ServletUriComponentsBuilder.fromCurrentContextPath()
                            .path(TwoFactorAuthenticationController.PATH)
                            .toUriString());
                return;
            } else {
                request.getSession().removeAttribute(CustomOAuth2RequestFactory.SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME);
            }
        }

        filterChain.doFilter(request, response);
    }

    private Map<String, String> paramsFromRequest(HttpServletRequest request) {
        Map<String, String> params = new HashMap<>();
        for (Entry<String, String[]> entry : request.getParameterMap().entrySet()) {
            params.put(entry.getKey(), entry.getValue()[0]);
        }
        return params;
    }
}

The TwoFactorAuthenticationController that handles entering the 2FA-code adds the authority ROLE_TWO_FACTOR_AUTHENTICATED if the code was correct and redirects the user back to the /oauth/authorize endpoint.

@Controller
@RequestMapping(TwoFactorAuthenticationController.PATH)
public class TwoFactorAuthenticationController {
    private static final Logger LOG = LoggerFactory.getLogger(TwoFactorAuthenticationController.class);

    public static final String PATH = "/secure/two_factor_authentication";

    @RequestMapping(method = RequestMethod.GET)
    public String auth(HttpServletRequest request, HttpSession session, ....) {
        if (AuthenticationUtil.isAuthenticatedWithAuthority(ROLE_TWO_FACTOR_AUTHENTICATED)) {
            LOG.info("User {} already has {} authority - no need to enter code again", ROLE_TWO_FACTOR_AUTHENTICATED);
            throw ....;
        }
        else if (session.getAttribute(CustomOAuth2RequestFactory.SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME) == null) {
            LOG.warn("Error while entering 2FA code - attribute {} not found in session.", CustomOAuth2RequestFactory.SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME);
            throw ....;
        }

        return ....; // Show the form to enter the 2FA secret
    }

    @RequestMapping(method = RequestMethod.POST)
    public String auth(....) {
        if (userEnteredCorrect2FASecret()) {
            AuthenticationUtil.addAuthority(ROLE_TWO_FACTOR_AUTHENTICATED);
            return "forward:/oauth/authorize"; // Continue with the OAuth flow
        }

        return ....; // Show the form to enter the 2FA secret again
    }
}

A custom OAuth2RequestFactory retrieves the previously saved AuthorizationRequest from the session if available and returns that or creates a new one if none can be found in the session.

/**
 * If the session contains an {@link AuthorizationRequest}, this one is used and returned.
 * The {@link com.example.TwoFactorAuthenticationFilter} saved the original AuthorizationRequest. This allows
 * to redirect the user away from the /oauth/authorize endpoint during oauth authorization
 * and show him e.g. a the page where he has to enter a code for two factor authentication.
 * Redirecting him back to /oauth/authorize will use the original authorizationRequest from the session
 * and continue with the oauth authorization.
 */
public class CustomOAuth2RequestFactory extends DefaultOAuth2RequestFactory {

    public static final String SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME = "savedAuthorizationRequest";

    public CustomOAuth2RequestFactory(ClientDetailsService clientDetailsService) {
        super(clientDetailsService);
    }

    @Override
    public AuthorizationRequest createAuthorizationRequest(Map<String, String> authorizationParameters) {
        ServletRequestAttributes attr = (ServletRequestAttributes) RequestContextHolder.currentRequestAttributes();
        HttpSession session = attr.getRequest().getSession(false);
        if (session != null) {
            AuthorizationRequest authorizationRequest = (AuthorizationRequest) session.getAttribute(SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME);
            if (authorizationRequest != null) {
                session.removeAttribute(SAVED_AUTHORIZATION_REQUEST_SESSION_ATTRIBUTE_NAME);
                return authorizationRequest;
            }
        }

        return super.createAuthorizationRequest(authorizationParameters);
    }
}

This custom OAuth2RequestFactory is set to the authorization server like:

<bean id="customOAuth2RequestFactory" class="com.example.CustomOAuth2RequestFactory">
    <constructor-arg index="0" ref="clientDetailsService" />
</bean>

<!-- Configures the authorization-server and provides the /oauth/authorize endpoint -->
<oauth:authorization-server client-details-service-ref="clientDetailsService" token-services-ref="tokenServices"
    user-approval-handler-ref="approvalStoreUserApprovalHandler" redirect-resolver-ref="redirectResolver"
    authorization-request-manager-ref="customOAuth2RequestFactory">
    <oauth:authorization-code authorization-code-services-ref="authorizationCodeServices"/>
    <oauth:implicit />
    <oauth:refresh-token />
    <oauth:client-credentials />
    <oauth:password />
</oauth:authorization-server>

When using java config you can create a TwoFactorAuthenticationInterceptor instead of the TwoFactorAuthenticationFilter and register it with an AuthorizationServerConfigurer with

@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfig implements AuthorizationServerConfigurer {
    ...

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {
        endpoints
            .addInterceptor(twoFactorAuthenticationInterceptor())
            ...
            .requestFactory(customOAuth2RequestFactory());
    }

    @Bean
    public HandlerInterceptor twoFactorAuthenticationInterceptor() {
        return new TwoFactorAuthenticationInterceptor();
    }
}

The TwoFactorAuthenticationInterceptor contains the same logic as the TwoFactorAuthenticationFilter in its preHandle method.