Open source OAuth2 desktop library for Java.

This library allows you to:

• Start an authorization code flow with PKCE, using the system's browser
• Get user info by access token
• Exchange a refresh token into new tokens

We had to write a native modular desktop application in Java where the user had to log in using Keycloak.

We were using the Keycloak Installed adapter, and that worked up until Keycloak version 16. The adapter redirected back to /delegated but that endpoint got removed in version 16. They didn't update the adapter. Our users would see a 404 after successfully logging in. That caused confusion.

Also, we had to hack modularity in the Keycloak Installed adapter, as it is not modular. Next to that, the adapter pulled in a lot of heavy dependencies like Undertow, JBoss RESTEasy, and whatnot. It also relied on Java EE, which has been deprecated since Java 9. Generating a jlink image was a pain.

We had to replace the Keycloak Installed adapter with something else, but what was available to use was either discontinued, not modular, or bloatware pulling in a lot of dependencies.

For our little needs, we decided it's better to write our own library with the following requirements:

• It has to be lightweight
• It needs to support Java modularity
• It should rely on as little as possible third-party dependencies
• It needs to be easy to use

This has only been tested using Keycloak as an authorization server.

If you are using Maven, add this to your pom.xml file:

<dependency>
  <groupId>com.giannivanhoecke.oauth</groupId>
  <artifactId>oauth-desktop</artifactId>
  <version>1.0</version>
</dependency>

If you are using Gradle, add this to your dependencies:

implementation 'com.giannivanhoecke.oauth:oauth-desktop:1.0'

In your module-info.java, add:

requires com.giannivanhoecke.oauth.desktop;

Start by configuring your authorization server using the default configuration:

AuthorizationServerConfig config = AuthorizationServerConfig
        .newBuilder()
        .withBaseUrl("http://localhost:8082/auth/realms/test/protocol/openid-connect")
        .withClientId("myclient")
        .build();

This will show a built-in HTML success page after authorization.

Alternatively, you can override the auth, userinfo, and token endpoints, as well as the scope:

AuthorizationServerConfig config = AuthorizationServerConfig
        .newBuilder()
        .withBaseUrl("http://localhost:8082/auth/realms/test/protocol/openid-connect")
        .withEndpointAuth("/auth")
        .withEndpointUserInfo("/userinfo")
        .withEndpointToken("/token")
        .withClientId("myclient")
        .withAuthScope("openid offline_access email profile")
        .withSuccessRedirectUri("http://localhost/success.html")
        .build();

The optional .withSuccessRedirectUri("http://localhost/success.html") will redirect to your page of choice instead of showing the built-in HTML success page.

Next, instantiate using the system's default browser:

authorizationCodeFlowWithPkce = new AuthorizationCodeFlowWithPkce(config);

Alternatively, you can supply your own Browser implementation, if the native Java Desktop isn't suitable for your use case:

authorizationCodeFlowWithPkce = new AuthorizationCodeFlowWithPkce(config, this::open);

To start the authorization flow using PKCE:

Future<AccessTokenResponse> accessTokenResponseFuture = authorizationCodeFlowWithPkce.authorize();
AccessTokenResponse accessTokenResponse = accessTokenResponseFuture.get(5, TimeUnit.MINUTES);

LOGGER.info("Success! I got:");
LOGGER.info("  -> access token:  " + accessTokenResponse.getAccessToken());
LOGGER.info("  -> refresh token: " + accessTokenResponse.getRefreshToken());

You will get a Future<AccessTokenResponse> instance, as we need to wait on an external action (the user authorizing in the browser).

In order to exchange a refresh token for new tokens:

AccessTokenResponse accessTokenResponse = authorizationCodeFlowWithPkce.refresh(refreshToken);

LOGGER.info("Success! I got:");
LOGGER.info("  -> access token:  " + accessTokenResponse.getAccessToken());
LOGGER.info("  -> refresh token: " + accessTokenResponse.getRefreshToken());

If you want retrieve some basic user info, or if you just want to test if your access token is still valid:

UserInfoResponse userInfoResponse = authorizationCodeFlowWithPkce.getUserInfo(accessToken);

LOGGER.info("Success! I got:");
LOGGER.info("  -> ID:       " + userInfoResponse.getId());
LOGGER.info("  -> Username: " + userInfoResponse.getUsername());
LOGGER.info("  -> Name:     " + userInfoResponse.getName());
LOGGER.info("  -> Email:    " + userInfoResponse.getEmail());

The OAuth2 Desktop Library throws unchecked exceptions. Check the JavaDocs for each method. If you want to catch all at once, it suffices to catch OAuth2Exception for any method.

MIT license - See LICENSE for more information.