Client (Authorization Code Flow)

In the second lab we want to build an OAuth2/OIDC client for the resource server we have built in lab 1. Therefore, you will be provided a complete spring mvc web client application that works together with the resource server of lab 1.

See Spring Security 5 OAuth 2.0 Client reference doc for all details on how to build and configure an OAuth 2.0 client.

Please check out the complete documentation for the sample application before starting with the first hands-on lab (especially the client side parts).

Lab Contents

Learning Targets

In Lab 2 we will use the OAuth2 authorization code grant flow to extend the provided web client to act as an OIDC compliant client.

The RFC 6749 specification describes this grant flow as follows:

The authorization code grant type is used to obtain both access tokens and refresh tokens and is optimized for confidential clients. Since this is a redirection-based flow, the client must be capable of interacting with the resource owner's user-agent (typically a web browser) and capable of receiving incoming requests (via redirection) from the authorization server.

The new draft for OAuth 2.0 Security Best Current Practice clearly recommends the use the authorization grant with PKCE. Although PKCE so far was designed as a mechanism to protect native apps, this advice applies to all kinds of OAuth clients, including public and confidential web applications.

This is why we also use the authorization code grant + PKCE flow here, even for a confidential client.

After you have completed this lab you will have learned

  • how to implement an OIDC compliant web client using the authorization code grant + PKCE flow

  • how to use the authenticated user principle (mapped from user info endpoint)

  • authorization on the client side (but only to hide/show buttons, real authorization must always be implemented on the server side)

Logout Users

After you have logged in into the library client using keycloak your session will remain valid until the access token has reached expiration, or the session at keycloak is invalidated.

Either you always open the web client in a private/incognito window of your web browser, or you follow the steps described below:

  • Login to keycloak admin console and navigate on the left to menu item session

    Here you'll see all user sessions (active/offline ones). By clicking on the button Logout all you can revoke

    all active sessions.

  • After you have revoked the sessions in keycloak you have to delete the current JSESSION cookie

    for the library client. You can do this by opening the application tab in the developer tools of chrome.

    Navigate to the cookies entry on the left and select the url of the library client, then delete the cookie

    on the right hand side

Now when you refresh the library client in the browser you should be redirected again to the login page of keycloak.

Folder Contents

In the folder lab 2 you find 2 applications:

  • library-client-initial: This is the client application we will use as starting point for this lab

  • library-client-complete: This client application is the completed OAuth 2.0/OIDC client reference for this lab

Start the Lab

Now, let's start with lab 2. Here we will implement the required additions to get an OAuth2/OIDC compliant client that calls the resource server we have implemented in lab 1.

We will use Keycloak as identity provider. Please again make sure you have set up keycloak as described in Setup Keycloak.

Explore the initial application

First start the resource server application of lab 1. If you could not complete the previous Lab yourself then use and start the completed reference application in project lab1/library-server-complete.

To start it you may also use the gradlew bootRun command.

Then navigate your Java IDE to the lab2/library-client-initial project and at first explore this project a bit. Then start the application by running the class com.example.library.client.Lab2LibraryClientInitialApplication.

To test if the application works as expected open a web browser and navigate to localhost:9090/library-client, when basic authentication popup appears use 'user' and 'secret' as login credentials.

Now you should see the message 'Not authenticated' as the library client only authenticates users for the client side using basic authentication but is not prepared to send the required bearer access token to the resource server.

Now stop the client application again. You can leave the resource server running as we will need this after we have finished this client.

Step 1: Configure as OAuth 2/OIDC client

To change this application into an OAuth2/OIDC client you have to make changes in the dependencies of the gradle build file build.gradle:

Remove this dependency:

implementation('org.springframework.boot:spring-boot-starter-security')

and add this dependency instead:

implementation('org.springframework.boot:spring-boot-starter-oauth2-client')

Note: Make sure to trigger a gradle update in your Java IDE

Spring security 5 utilizes the OpenID Connect Discovery specification to completely configure the client to work together with the Keycloak instance.

Make sure keycloak has been started as described in the setup section.

Navigate your web browser to the url localhost:8080/auth/realms/workshop/.well-known/openid-configuration. Then you should see the public discovery information that keycloak provides (similar to the following snippet, showing only partial information).

{
  "issuer": "http://localhost:8080/auth/realms/workshop",
  "authorization_endpoint": "http://localhost:8080/auth/realms/workshop/protocol/openid-connect/auth",
  "token_endpoint": "http://localhost:8080/auth/realms/workshop/protocol/openid-connect/token",
  "userinfo_endpoint": "http://localhost:8080/auth/realms/workshop/protocol/openid-connect/userinfo",
  "jwks_uri": "http://localhost:8080/auth/realms/workshop/protocol/openid-connect/certs"
}

For configuring an OAuth2 client the important entries are issuer, authorization_endpoint, token_endpoint, userinfo_endpoint and jwks_uri. Spring Security 5 automatically configures an OAuth2 client by just specifying the issuer uri value as part of the predefined spring property spring.security.oauth2.client.provider.[id].issuer-uri.

For OAuth2 clients you have to specify the client registration, which usually consists of client id, client secret, authorization grant type, redirect uri to your client callback and optionally the scope. With Spring Security 5.2.0 you can use the authorization code grant with PKCE. This is the recommend grant type for this kind of application meanwhile. (see https://tools.ietf.org/html/draft-ietf-oauth-security-topics-13#section-3.1.1)

To make use of this grant type, make sure you have a public client and just omit the client secret. If you want to make sure PKCE is being used, you can specify client-authentication-method to none. (as in the code below)

The client registration requires an OAuth2 provider. If you want to use your own provider you have to configure at least the issuer uri. We want to change the default user name mapping for the user identity as well ( using the user name instead of the default value 'sub').

To perform this step, open application.yml_ and add the issuer uri property with the additional ones. Please remove the existing entry for (user.password) as we don't need this anymore.

After adding this it should look like this:

spring:
  thymeleaf:
    cache: false
  security:
    oauth2:
      client:
        registration:
          keycloak:
            client-id: 'library-client-pkce'
            authorizationGrantType: authorization_code
            redirect-uri: '{baseUrl}/login/oauth2/code/{registrationId}'
            client-authentication-method: none
            scope: openid
        provider:
          keycloak:
            issuerUri: http://localhost:8080/auth/realms/workshop
            user-name-attribute: name

An error you get very often with files in yaml format is that the indents are not correct. This can lead to unexpected errors later when you try to run all this stuff.

Step 2: Configure web client to send bearer access token

For all requests to the resource server we use the reactive web client, that was introduced by Spring 5. The next required step is to make this web client aware of transmitting the required bearer access tokens in the Authorization header.

To achieve this open the class com.example.library.client.config.WebClientConfiguration and reconfigure the web client as follows:

package com.example.library.client.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.oauth2.client.registration.ClientRegistrationRepository;
import org.springframework.security.oauth2.client.web.OAuth2AuthorizedClientRepository;
import org.springframework.security.oauth2.client.web.reactive.function.client.ServletOAuth2AuthorizedClientExchangeFilterFunction;
import org.springframework.web.reactive.function.client.WebClient;

@Configuration
public class WebClientConfiguration {

  @Bean
  WebClient webClient(
      ClientRegistrationRepository clientRegistrations,
      OAuth2AuthorizedClientRepository authorizedClients) {
    ServletOAuth2AuthorizedClientExchangeFilterFunction oauth2 =
        new ServletOAuth2AuthorizedClientExchangeFilterFunction(
            clientRegistrations, authorizedClients);
    oauth2.setDefaultOAuth2AuthorizedClient(true);
    oauth2.setDefaultClientRegistrationId("keycloak");
    return WebClient.builder().apply(oauth2.oauth2Configuration()).build();
  }
}

With these additions we add a filter function to the web client that automatically adds the access token to all requests and initiates the authorization grant flow if no valid access token is available.

Step 3: Configure web client authorities

Same as on resource server side we don't want to use the automatic SCOPE_xxx authorities but instead want to map again the groups claim we get from the automatically called userinfo endpoint to the expected ROLE_xxx authorities.

To achieve this we have to extend the class com.example.library.client.config.WebSecurityConfiguration:

package com.example.library.client.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.authority.SimpleGrantedAuthority;
import org.springframework.security.core.authority.mapping.GrantedAuthoritiesMapper;
import org.springframework.security.oauth2.core.oidc.OidcIdToken;
import org.springframework.security.oauth2.core.oidc.OidcUserInfo;
import org.springframework.security.oauth2.core.oidc.user.OidcUserAuthority;

import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

@Configuration
public class WebSecurityConfiguration extends WebSecurityConfigurerAdapter {

  @Override
  protected void configure(HttpSecurity http) throws Exception {
    http.authorizeRequests()
        .anyRequest()
        .fullyAuthenticated()
        .and()
        .oauth2Client()
        .and()
        .oauth2Login()
        .userInfoEndpoint()
        .userAuthoritiesMapper(userAuthoritiesMapper());
  }

  private GrantedAuthoritiesMapper userAuthoritiesMapper() {
    return (authorities) -> {
      Set<GrantedAuthority> mappedAuthorities = new HashSet<>();

      authorities.forEach(
          authority -> {
            if (authority instanceof OidcUserAuthority) {
              OidcUserAuthority oidcUserAuthority = (OidcUserAuthority) authority;

              OidcIdToken idToken = oidcUserAuthority.getIdToken();
              OidcUserInfo userInfo = oidcUserAuthority.getUserInfo();

              List<SimpleGrantedAuthority> groupAuthorities =
                  userInfo.getClaimAsStringList("groups").stream()
                      .map(g -> new SimpleGrantedAuthority("ROLE_" + g.toUpperCase()))
                      .collect(Collectors.toList());
              mappedAuthorities.addAll(groupAuthorities);
            }
          });

      return mappedAuthorities;
    };
  }
}

With the snippet

...
.oauth2Client()
        .and()
        .oauth2Login()
        .userInfoEndpoint()
        .userAuthoritiesMapper(userAuthoritiesMapper());

we configure an OAuth2 client and an OIDC login client and reconfigure the userinfo endpoint user mapping to map authorities different as the standard one. The custom mapping is performed in the implementation of the GrantedAuthoritiesMapper interface that maps entries of the groups claim to spring security authority roles.

Step 4: Change authentication principal

The final required step is to change the authentication principal from org.springframework.security.core.userdetails.User to org.springframework.security.oauth2.core.oidc.user.OidcUser.

We have to change this in class com.example.library.client.web.BookResource:

import org.springframework.security.oauth2.core.oidc.user.OidcUser;
...
public boolean returnBookAllowed(OidcUser user) {
    if (!isBorrowed()) {
      return false;
    }

    if (user != null) {
      return borrowedBy != null && borrowedBy.getEmail().equals(user.getEmail());
    } else {
      // Always fail secure
      return false;
    }
}
...

and in class com.example.library.client.web.BooksController:

    import net.minidev.json.JSONArray;
    import org.springframework.security.oauth2.core.user.OAuth2User;
    ...
    @GetMapping("/")
      Mono<String> index(@AuthenticationPrincipal OidcUser oidcUser, Model model) {

        model.addAttribute("fullname", oidcUser.getName());
        model.addAttribute(
            "isCurator",
            ((JSONArray) oidcUser.getClaim("groups")).get(0).equals("library_curator"));
        ...    
    }    
    ...

Step 5: Run/debug the OAuth2 web client application

Now re-start the library client using gradlew bootRun command and browse again to localhost:9090/library-client and login using the different users:

Now, after authenticating at keycloak you should be able to see the library client.

Please also checkout what happens if you log in with users having different roles, e.g. as pparker as the library curator.

If you want to see what is going on behind the scenes just add some debugging breakpoints to the following classes and methods.

Authorization Request:

For this part add a debugging breakpoint to the method

OAuth2AuthorizationRequest resolve(HttpServletRequest request, String registrationId, String redirectUriAction) in class org.springframework.security.oauth2.client.web.DefaultOAuth2AuthorizationRequestResolver.

Authorization code redirect callback:

For this part add a debugging breakpoint to the method

Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response) in class org.springframework.security.oauth2.client.web.OAuth2LoginAuthenticationFilter

Exchange authorization code for access token:

For this part add a debugging breakpoint to the method

OAuth2AccessTokenResponse getTokenResponse(OAuth2AuthorizationCodeGrantRequest authorizationCodeGrantRequest) in class org.springframework.security.oauth2.client.endpoint.DefaultAuthorizationCodeTokenResponseClient

That's a wrap for this second Lab.

In the Lab 3 we continue to implement almost again an OAuth2 client but this time we are using another OAuth2 grant flow: The client credentials flow.

PreviousResource ServerNextClient (Client Credentials Flow)

Last updated