OAuth RFC-8628 Device Code Grant Flow (#4632)

Signed-off-by: Andrew Fiddian-Green <software@whitebear.ch>
2026-07-29 12:34:22 +02:00 · 2025-03-17 00:40:07 +01:00
parent 8de8b4d4b4
commit 2eec58a95f
9 changed files with 1209 additions and 13 deletions
@@ -31,6 +31,7 @@ import org.eclipse.jetty.util.Fields;
 import org.eclipse.jetty.util.UrlEncoded;
 import org.openhab.core.auth.client.oauth2.AccessTokenRefreshListener;
 import org.openhab.core.auth.client.oauth2.AccessTokenResponse;
+import org.openhab.core.auth.client.oauth2.DeviceCodeResponseDTO;
 import org.openhab.core.auth.client.oauth2.OAuthClientService;
 import org.openhab.core.auth.client.oauth2.OAuthException;
 import org.openhab.core.auth.client.oauth2.OAuthResponseException;
@@ -77,6 +78,7 @@ public class OAuthClientServiceImpl implements OAuthClientService {
    private PersistedParams persistedParams = new PersistedParams();

    private @Nullable Fields extraAuthFields = null;
+    private @Nullable OAuthConnectorRFC8628 oAuthConnectorRFC8628 = null;

    private volatile boolean closed = false;

@@ -392,8 +394,16 @@ public class OAuthClientServiceImpl implements OAuthClientService {
    public void close() {
        closed = true;
        storeHandler = null;
-
        logger.debug("closing oauth client, handle: {}", handle);
+        closeOAuthConnectorRFC8628();
+    }
+
+    private synchronized void closeOAuthConnectorRFC8628() {
+        OAuthConnectorRFC8628 connector = this.oAuthConnectorRFC8628;
+        if (connector != null) {
+            connector.close();
+        }
+        this.oAuthConnectorRFC8628 = null;
    }

    @Override
@@ -440,4 +450,34 @@ public class OAuthClientServiceImpl implements OAuthClientService {

        return clientService;
    }
+
+    @Override
+    public @Nullable DeviceCodeResponseDTO getDeviceCodeResponse() throws OAuthException {
+        closeOAuthConnectorRFC8628();
+
+        if (persistedParams.tokenUrl == null) {
+            throw new OAuthException("Missing access token request url");
+        }
+        if (persistedParams.authorizationUrl == null) {
+            throw new OAuthException("Missing device code request url");
+        }
+        if (persistedParams.clientId == null) {
+            throw new OAuthException("Missing client id");
+        }
+        if (persistedParams.scope == null) {
+            throw new OAuthException("Missing scope");
+        }
+
+        OAuthConnectorRFC8628 connector = new OAuthConnectorRFC8628(this, handle, storeHandler, httpClientFactory,
+                gsonBuilder, persistedParams.tokenUrl, persistedParams.authorizationUrl, persistedParams.clientId,
+                persistedParams.scope);
+
+        oAuthConnectorRFC8628 = connector;
+        return connector.getDeviceCodeResponse();
+    }
+
+    @Override
+    public void notifyAccessTokenResponse(AccessTokenResponse atr) {
+        accessTokenRefreshListeners.forEach(l -> l.onAccessTokenResponse(atr));
+    }
 }
@@ -62,12 +62,13 @@ public class OAuthConnector {

    private static final String HTTP_CLIENT_CONSUMER_NAME = "OAuthConnector";

-    private final HttpClientFactory httpClientFactory;
+    protected final HttpClientFactory httpClientFactory;

    private final @Nullable Fields extraFields;

    private final Logger logger = LoggerFactory.getLogger(OAuthConnector.class);
-    private final Gson gson;
+
+    protected final Gson gson;

    public OAuthConnector(HttpClientFactory httpClientFactory) {
        this(httpClientFactory, null, new GsonBuilder());
@@ -371,7 +372,7 @@ public class OAuthConnector {
     * @throws OAuthException If any exception is thrown while starting the http client.
     * @see org.openhab.core.io.net.http.ExtensibleTrustManager
     */
-    private HttpClient createHttpClient(String tokenUrl) throws OAuthException {
+    protected HttpClient createHttpClient(String tokenUrl) throws OAuthException {
        HttpClient httpClient = httpClientFactory.createHttpClient(HTTP_CLIENT_CONSUMER_NAME);
        if (!httpClient.isStarted()) {
            try {
@@ -383,7 +384,7 @@ public class OAuthConnector {
        return httpClient;
    }

-    private void shutdownQuietly(@Nullable HttpClient httpClient) {
+    protected void shutdownQuietly(@Nullable HttpClient httpClient) {
        try {
            if (httpClient != null) {
                httpClient.stop();
@@ -0,0 +1,474 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.auth.oauth2client.internal;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+import java.time.Instant;
+import java.util.Objects;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+import org.eclipse.jetty.client.HttpClient;
+import org.eclipse.jetty.client.api.ContentResponse;
+import org.eclipse.jetty.client.api.Request;
+import org.eclipse.jetty.http.HttpMethod;
+import org.eclipse.jetty.http.HttpStatus;
+import org.openhab.core.auth.client.oauth2.AccessTokenResponse;
+import org.openhab.core.auth.client.oauth2.DeviceCodeResponseDTO;
+import org.openhab.core.auth.client.oauth2.OAuthClientService;
+import org.openhab.core.auth.client.oauth2.OAuthException;
+import org.openhab.core.auth.client.oauth2.OAuthResponseException;
+import org.openhab.core.common.ThreadPoolManager;
+import org.openhab.core.io.net.http.HttpClientFactory;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.gson.GsonBuilder;
+
+/**
+ * The {@link OAuthConnectorRFC8628} extends {@link OAuthConnector} to implement
+ * the oAuth RFC-8628 Device Code Grant Flow authentication process.
+ *
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc8628">RFC-8628</a>
+ *
+ * @author Andrew Fiddian-Green - Initial contribution
+ */
+@NonNullByDefault
+public class OAuthConnectorRFC8628 extends OAuthConnector implements AutoCloseable {
+
+    private static final String OAUTH_RFC8628 = "oauth-rfc8628";
+
+    // URL parameter names
+    private static final String PARAM_SCOPE = "scope";
+    private static final String PARAM_CLIENT_ID = "client_id";
+    private static final String PARAM_DEVICE_CODE = "device_code";
+    private static final String PARAM_GRANT_TYPE = "grant_type";
+
+    // HTTP 400 error messages for RFC-8628
+    private static final String SLOW_DOWN = "slow_down";
+    private static final String ACCESS_DENIED = "access_denied";
+    private static final String EXPIRED_TOKEN = "expired_token";
+
+    // URL parameter values
+    private static final String PARAM_GRANT_TYPE_VALUE = "urn:ietf:params:oauth:grant-type:device_code";
+
+    // logger string
+    private static final String LOG_NULL_ATR = "AccessTokenResponse [null]";
+
+    private static final int HTTP_TIMEOUT_MILLISECONDS = 5000;
+    private static final long DEFAULT_POLL_INTERVAL = 5;
+
+    private final Logger logger = LoggerFactory.getLogger(OAuthConnectorRFC8628.class);
+
+    private final OAuthClientService oAuthClientService;
+    private final OAuthStoreHandler oAuthStoreHandler;
+    private final ScheduledExecutorService scheduler;
+    private final String handle;
+
+    private final String accessTokenRequestUrl;
+    private final String deviceCodeRequestUrl;
+    private final String clientIdParameter;
+    private final String scopeParameter;
+
+    private @Nullable ScheduledFuture<?> atrPollTaskSchedule;
+    private @Nullable DeviceCodeResponseDTO dcrCached;
+    private @Nullable HttpClient httpClient;
+
+    /**
+     * Create an extension of the {link OAuthConnector} that implements the oAuth RFC-8628 Device Code
+     * Grant Flow authentication process. The parameters are as follows -- whereby (*) means that the
+     * parameters would usually be from the private fields of the calling {@link OAuthClientService}.
+     *
+     * @param oAuthClientService the calling {@link OAuthClientService}
+     * @param handle an oAuth storage handle (*)
+     * @param oAuthStoreHandler a {@link OAuthStoreHandler} (*)
+     * @param httpClientFactory a {@link HttpClientFactory} (*)
+     * @param gsonBuilder a {@link GsonBuilder} (may be null) (*)
+     * @param accessTokenRequestUrl the URL that provides {@link AccessTokenResponse} responses
+     * @param deviceCodeRequestUrl the URL that provides {@link DeviceCodeResponseDTO} responses
+     * @param clientId the RFC-8628 request client id parameter
+     * @param scope the RFC-8628 request scope parameter
+     *
+     * @throws OAuthException
+     */
+    public OAuthConnectorRFC8628(OAuthClientService oAuthClientService, String handle,
+            OAuthStoreHandler oAuthStoreHandler, HttpClientFactory httpClientFactory, @Nullable GsonBuilder gsonBuilder,
+            String accessTokenRequestUrl, String deviceCodeRequestUrl, String clientId, String scope)
+            throws OAuthException {
+        super(httpClientFactory, null, gsonBuilder != null ? gsonBuilder : new GsonBuilder());
+        this.oAuthClientService = oAuthClientService;
+        this.oAuthStoreHandler = oAuthStoreHandler;
+        this.scheduler = ThreadPoolManager.getScheduledPool(OAUTH_RFC8628);
+        this.deviceCodeRequestUrl = deviceCodeRequestUrl;
+        this.accessTokenRequestUrl = accessTokenRequestUrl;
+        this.clientIdParameter = clientId;
+        this.scopeParameter = scope;
+        this.handle = handle;
+    }
+
+    /**
+     * Begins the RFC-8628 Device Code Grant Flow authentication process.
+     * Specifically it executes the following steps as described in the article in the link below:
+     *
+     * <ul>
+     * <li>Step 1: create a request and POST it to the 'device authorize url'</li>
+     * <li>Step 2: process the response and create a {@link DeviceCodeResponseDTO}</li>
+     * <li>Step 3: the user goes off to authenticate themselves at the 'user authentication url'</li>
+     * <li>Step 4: repeatedly create a request and POST it to the 'token url'</li>
+     * <li>Step 5: repeatedly read the response and eventually create a {@link AccessTokenResponse}</li>
+     * </ul>
+     *
+     * @see <a href="https://datatracker.ietf.org/doc/html/rfc8628">RFC-8628</a>
+     *
+     * @return either null or a {@link DeviceCodeResponseDTO} containing the verification uri's where
+     *         users are expected authenticate themselves
+     * @throws OAuthException
+     */
+    public synchronized @Nullable DeviceCodeResponseDTO getDeviceCodeResponse() throws OAuthException {
+        /*
+         * 'finally' control variable to create a poll task schedule with the given interval
+         */
+        long createNewAtrPollTaskScheduleSeconds = 0;
+        try {
+            logger.trace("getDeviceCodeResponse() start..");
+            if (oAuthClientService.isClosed()) {
+                /*
+                 * The service is closed:
+                 * => throw an exception
+                 */
+                throw new OAuthException("OAuthClientService closed");
+            }
+
+            /*
+             * Retrieve local AccessTokenResponse from service (if any)
+             */
+            AccessTokenResponse atr;
+            try {
+                atr = oAuthClientService.getAccessTokenResponse();
+            } catch (IOException | OAuthResponseException e) {
+                atr = null;
+            }
+            logger.trace("getDeviceCodeResponse() loaded from service: {}", atr != null ? atr : LOG_NULL_ATR);
+
+            if (atr != null) {
+                /*
+                 * The local AccessTokenResponse exists:
+                 * => no further user authentication is needed
+                 * => return null
+                 */
+                return null;
+            }
+
+            DeviceCodeResponseDTO dcr;
+            try {
+                /*
+                 * Load local DeviceCodeResponse from service storage (if any) and check it is valid
+                 */
+                dcr = checkDeviceCodeResponse(oAuthStoreHandler.loadDeviceCodeResponse(handle));
+                logger.trace("getDeviceCodeResponse() loaded from storage: {}", dcr);
+            } catch (GeneralSecurityException e) {
+                throw new OAuthException(e);
+            } catch (OAuthException e) {
+                /*
+                 * The DeviceCodeResponse is not valid
+                 * => try to fetch a new one from the remote server and check it is valid
+                 * => note: a second OAuthException exits from this method with that exception
+                 */
+                dcr = checkDeviceCodeResponse(fetchDeviceCodeResponse());
+                logger.trace("getDeviceCodeResponse() fetched from remote: {}", dcr);
+            }
+
+            /*
+             * If we got here without exception then the (local or remote) DeviceCodeResponse is all good:
+             * => try to fetch an AccessTokenResponse for it from the remote server
+             * => if the fetch fails-soft (authentication not yet done) it returns a null AccessTokenResponse
+             * => if the fetch fails-hard it throws an exception
+             */
+            try {
+                atr = fetchAccessTokenResponse(dcr);
+            } catch (OAuthResponseException e) {
+                /*
+                 * An AccessTokenResponse was not returned
+                 * => so atr remains null; as it was prior to calling fetchAccessTokenResponse()
+                 */
+            }
+            logger.trace("getDeviceCodeResponse() fetched from remote: {}", atr != null ? atr : LOG_NULL_ATR);
+
+            if (atr != null) {
+                /*
+                 * The fetched AccessTokenResponse exists:
+                 * => import the AccessTokenResponse into the service storage
+                 * => notify service AccessTokenRefreshListeners
+                 * => no further user authentication is needed
+                 * => exit by returning null
+                 */
+                oAuthClientService.importAccessTokenResponse(atr);
+                oAuthClientService.notifyAccessTokenResponse(atr);
+                logger.trace("getDeviceCodeResponse() imported into service: {}", atr);
+                return null;
+            }
+
+            /*
+             * If we got to this point we have a good DeviceCodeResponse but AccessTokenResponse is null:
+             * => cache the DeviceCodeResponse across polling cycles
+             * => save the DeviceCodeResponse in the service storage
+             * => schedule a new AccessTokenResponse poll task
+             * => return the DeviceCodeResponse
+             */
+            logger.trace("getDeviceCodeResponse() service save, cache, schedule poll, return: {}", dcr);
+            createNewAtrPollTaskScheduleSeconds = Objects.requireNonNull(dcr.getInterval());
+            oAuthStoreHandler.saveDeviceCodeResponse(handle, dcr);
+            dcrCached = dcr;
+            return (DeviceCodeResponseDTO) dcr.clone();
+        } catch (OAuthException e) {
+            logger.debug("getDeviceCodeResponse() error: {}", e.getMessage());
+            createNewAtrPollTaskScheduleSeconds = 0;
+            throw e;
+        } finally {
+            if (createNewAtrPollTaskScheduleSeconds > 0) {
+                cancelAtrPollTaskSchedule();
+                createAtrPollTaskSchedule(createNewAtrPollTaskScheduleSeconds);
+            } else {
+                close();
+            }
+        }
+    }
+
+    /**
+     * Check the validity of the given {@link DeviceCodeResponseDTO}
+     *
+     * @param dcr the incoming {@link DeviceCodeResponseDTO} (may be null)
+     * @return a fully valid {@link DeviceCodeResponseDTO} (guaranteed non null)
+     *
+     * @throws OAuthException
+     */
+    private DeviceCodeResponseDTO checkDeviceCodeResponse(@Nullable DeviceCodeResponseDTO dcr) throws OAuthException {
+        if (dcr == null) {
+            throw new OAuthException("DeviceCodeResponse is null");
+        }
+        if (dcr.isExpired(Instant.now(), 0)) {
+            throw new OAuthException("DeviceCodeResponse expired");
+        }
+        Long interval = dcr.getInterval();
+        if (interval == null || interval <= 0) {
+            throw new OAuthException("DeviceCodeResponse interval invalid");
+        }
+        return dcr;
+    }
+
+    /**
+     * Start the first steps of the Device Code Grant Flow authentication process as follows:
+     *
+     * <ul>
+     * <li>Step 1: create a request and POST it to the authentication (device code) url</li>
+     * <li>Step 2: process the response and create a {@link DeviceCodeResponseDTO}</li>
+     * </ul>
+     *
+     * @return a new {@link DeviceCodeResponseDTO} object (non null)
+     *
+     * @throws OAuthException
+     */
+    private synchronized DeviceCodeResponseDTO fetchDeviceCodeResponse() throws OAuthException {
+        Request request = createHttpClient().newRequest(deviceCodeRequestUrl);
+        request.method(HttpMethod.POST);
+        request.timeout(HTTP_TIMEOUT_MILLISECONDS, TimeUnit.MILLISECONDS);
+        request.param(PARAM_CLIENT_ID, clientIdParameter);
+        request.param(PARAM_SCOPE, scopeParameter);
+        logger.trace("fetchDeviceCodeResponse() request: {}", request.getURI());
+
+        try {
+            ContentResponse response = request.send();
+            String content = response.getContentAsString();
+            logger.trace("fetchDeviceCodeResponse() response: {}", content);
+
+            if (response.getStatus() == HttpStatus.OK_200) {
+                DeviceCodeResponseDTO dcr = gson.fromJson(content, DeviceCodeResponseDTO.class);
+                if (dcr != null) {
+                    dcr.setCreatedOn(Instant.now());
+                    // in RFC-8628 'interval' is OPTIONAL so if absent use default
+                    if (dcr.getInterval() == null) {
+                        dcr.setInterval(DEFAULT_POLL_INTERVAL);
+                    }
+                    logger.trace("fetchDeviceCodeResponse() return: {}", dcr);
+                    return dcr;
+                }
+            }
+            throw new OAuthException("fetchDeviceCodeResponse() error: " + response);
+        } catch (InterruptedException | TimeoutException | ExecutionException e) {
+            throw new OAuthException("fetchDeviceCodeResponse() error", e);
+        }
+    }
+
+    /**
+     * Whilst the user is completing the Device Code Grant Flow authentication process step 3
+     * we continue, in parallel, the completion of the authentication process by repeating the
+     * following steps:
+     *
+     * <ul>
+     * <li>Step 4: repeatedly create a request and POST it to the access token url</li>
+     * <li>Step 5: repeatedly read the response and eventually create a {@link AccessTokenResponse}</li>
+     * </ul>
+     *
+     * @param dcr the {@link DeviceCodeResponseDTO}
+     *
+     * @return an {@link AccessTokenResponse} object or null
+     * @throws OAuthResponseException if the response content is an OAuth JSON error packet
+     * @throws OAuthException for any other errors
+     */
+    private synchronized @Nullable AccessTokenResponse fetchAccessTokenResponse(DeviceCodeResponseDTO dcr)
+            throws OAuthException, OAuthResponseException {
+        Request request = createHttpClient().newRequest(accessTokenRequestUrl);
+        request.method(HttpMethod.POST);
+        request.timeout(HTTP_TIMEOUT_MILLISECONDS, TimeUnit.MILLISECONDS);
+        request.param(PARAM_CLIENT_ID, clientIdParameter);
+        request.param(PARAM_GRANT_TYPE, PARAM_GRANT_TYPE_VALUE);
+        request.param(PARAM_DEVICE_CODE, dcr.getDeviceCode());
+        logger.trace("fetchAccessTokenResponse() request: {}", request.getURI());
+
+        try {
+            ContentResponse response = request.send();
+            String content = response.getContentAsString();
+            logger.trace("fetchAccessTokenResponse() response: {}", content);
+
+            switch (response.getStatus()) {
+                case HttpStatus.OK_200:
+                    AccessTokenResponse atr = gson.fromJson(content, AccessTokenResponse.class);
+                    if (atr != null) {
+                        atr.setCreatedOn(Instant.now());
+                        logger.trace("fetchAccessTokenResponse() return: {}", atr);
+                        return atr;
+                    }
+                case HttpStatus.BAD_REQUEST_400:
+                    OAuthResponseException err = gson.fromJson(content, OAuthResponseException.class);
+                    if (err != null) {
+                        throw err;
+                    }
+            }
+
+            /*
+             * Return null without throwing an exception since other HTTP responses
+             * may occur during AccessTokenResponse polling before the user has
+             * completed the verification process
+             */
+            return null;
+        } catch (InterruptedException | TimeoutException | ExecutionException e) {
+            throw new OAuthException("fetchAccessTokenResponse() error", e);
+        }
+    }
+
+    @Override
+    public void close() {
+        dcrCached = null;
+        cancelAtrPollTaskSchedule();
+        closeHttpClient();
+    }
+
+    private synchronized void cancelAtrPollTaskSchedule() {
+        ScheduledFuture<?> future = atrPollTaskSchedule;
+        if (future != null) {
+            future.cancel(false);
+            logger.trace("cancelAtrPollTaskSchedule() cancelled schedule of poll tasks");
+        }
+        atrPollTaskSchedule = null;
+    }
+
+    private void closeHttpClient() {
+        shutdownQuietly(httpClient);
+        httpClient = null;
+    }
+
+    private void createAtrPollTaskSchedule(long seconds) {
+        atrPollTaskSchedule = scheduler.scheduleWithFixedDelay(() -> atrPollTask(), seconds, seconds, TimeUnit.SECONDS);
+        logger.trace("createAtrPollTaskSchedule() created schedule of poll tasks every {}s", seconds);
+    }
+
+    private HttpClient createHttpClient() throws OAuthException {
+        HttpClient httpClient = this.httpClient;
+        if (httpClient == null) {
+            httpClient = createHttpClient(OAUTH_RFC8628);
+            this.httpClient = httpClient;
+        }
+        return httpClient;
+    }
+
+    /**
+     * This method is called repeatedly on the scheduler to poll for an {@link AccessTokenResponse}.
+     * It cancels its own scheduler when either a) an AccessTokenResponse is returned, or b) the
+     * cached {@link DeviceCodeResponseDTO} expires.
+     */
+    private synchronized void atrPollTask() {
+        /*
+         * 'finally' control variable to cancel the poll task schedule and close the http client
+         */
+        boolean close = false;
+        try {
+            DeviceCodeResponseDTO dcr = dcrCached;
+            logger.trace("atrPollTask() started with cached: {}", dcr);
+            try {
+                dcr = checkDeviceCodeResponse(dcr);
+
+                /*
+                 * The cached DeviceCodeResponse is still valid:
+                 * => get an AccessTokenResponse from it
+                 * => in case of error, cancel the polling schedule
+                 */
+                AccessTokenResponse atr = fetchAccessTokenResponse(dcr);
+                logger.trace("atrPollTask() fetched from remote: {}", atr);
+
+                if (atr != null) {
+                    /*
+                     * The AccessTokenResponse is OK:
+                     * => import the AccessTokenResponse into the service
+                     * => notify service AccessTokenRefreshListeners
+                     * => cancel the polling schedule
+                     */
+                    oAuthClientService.importAccessTokenResponse(atr);
+                    oAuthClientService.notifyAccessTokenResponse(atr);
+                    logger.trace("atrPollTask() imported into service: {}", atr);
+                    close = true;
+                }
+            } catch (OAuthResponseException e) {
+                String error = e.getError();
+                logger.trace("atrPollTask() poll response error: {}", error);
+                switch (error) {
+                    case ACCESS_DENIED, EXPIRED_TOKEN:
+                        close = true;
+                        break;
+
+                    case SLOW_DOWN:
+                        ScheduledFuture<?> future = atrPollTaskSchedule;
+                        if (future != null) {
+                            long priorDelay = future.getDelay(TimeUnit.SECONDS);
+                            cancelAtrPollTaskSchedule();
+                            createAtrPollTaskSchedule(priorDelay + 1);
+                        }
+                        break;
+                }
+            } catch (OAuthException e) {
+                logger.debug("atrPollTask() error: {}", e.getMessage());
+                close = true;
+            }
+        } finally {
+            if (close) {
+                close();
+            }
+            logger.trace("atrPollTask() done");
+        }
+    }
+}
@@ -17,11 +17,13 @@ import java.security.GeneralSecurityException;
 import org.eclipse.jdt.annotation.NonNullByDefault;
 import org.eclipse.jdt.annotation.Nullable;
 import org.openhab.core.auth.client.oauth2.AccessTokenResponse;
+import org.openhab.core.auth.client.oauth2.DeviceCodeResponseDTO;

 /**
 * This is for OAuth client internal use.
 *
 * @author Gary Tse - Initial contribution
+ * @author Andrew Fiddian-Green - added RFC-8628 support
 */
@NonNullByDefault
 public interface OAuthStoreHandler {
@@ -50,6 +52,30 @@ public interface OAuthStoreHandler {
     */
    void saveAccessTokenResponse(String handle, @Nullable AccessTokenResponse accessTokenResponse);

+    /**
+     * Get a {@link DeviceCodeResponseDTO} from the store. The device code is encrypted and therefore will be decrypted
+     * before returning.
+     *
+     * If the storage is not available, it is still possible to get the DeviceCodeResponse from memory cache.
+     * However, the last-used statistics will be broken. It is a measured risk to take.
+     *
+     * @param handle the handle given by the call
+     *            {@code OAuthFactory#createOAuthClientService(String, String, String, String, String, Boolean)}
+     * @return DeviceCodeResponse if available, null if not.
+     * @throws GeneralSecurityException when the token cannot be decrypted.
+     */
+    @Nullable
+    DeviceCodeResponseDTO loadDeviceCodeResponse(String handle) throws GeneralSecurityException;
+
+    /**
+     * Save the {@code DeviceCodeResponse} by the handle
+     *
+     * @param handle unique string used as a handle/ reference to the OAuth client service, and the underlying
+     *            access tokens, configs.
+     * @param deviceCodeResponse This can be null, which explicitly removes the DeviceCodeResponse from store.
+     */
+    void saveDeviceCodeResponse(String handle, @Nullable DeviceCodeResponseDTO deviceCodeResponse);
+
    /**
     * Remove the token for the given handler. No exception is thrown in all cases
     *
@@ -33,6 +33,7 @@ import java.util.concurrent.locks.ReentrantLock;
 import org.eclipse.jdt.annotation.NonNullByDefault;
 import org.eclipse.jdt.annotation.Nullable;
 import org.openhab.core.auth.client.oauth2.AccessTokenResponse;
+import org.openhab.core.auth.client.oauth2.DeviceCodeResponseDTO;
 import org.openhab.core.auth.client.oauth2.StorageCipher;
 import org.openhab.core.auth.oauth2client.internal.cipher.SymmetricKeyCipher;
 import org.openhab.core.library.types.DateTimeType;
@@ -51,6 +52,7 @@ import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializer;
 import com.google.gson.JsonPrimitive;
 import com.google.gson.JsonSerializer;
+import com.google.gson.JsonSyntaxException;

 /**
 * This class handles the storage directly. It is internal to the OAuthClientService and there is
@@ -73,6 +75,7 @@ import com.google.gson.JsonSerializer;
 * The recycle is performed when then instance is deactivated
 *
 * @author Gary Tse - Initial contribution
+ * @author Andrew Fiddian-Green - added RFC-8628 support
 */
@NonNullByDefault
@Component(property = "CIPHER_TARGET=SymmetricKeyCipher")
@@ -148,6 +151,33 @@ public class OAuthStoreHandlerImpl implements OAuthStoreHandler {
        storageFacade.put(handle, encryptedToken);
    }

+    @Override
+    public @Nullable DeviceCodeResponseDTO loadDeviceCodeResponse(String handle) throws GeneralSecurityException {
+        DeviceCodeResponseDTO dcr = (DeviceCodeResponseDTO) storageFacade.get(handle, DEVICE_CODE_RESPONSE);
+        if (dcr == null) {
+            // device code response does not exist
+            return null;
+        }
+        return decryptDeviceCodeResponse(dcr);
+    }
+
+    @Override
+    public void saveDeviceCodeResponse(String handle, @Nullable DeviceCodeResponseDTO dcrArg) {
+        DeviceCodeResponseDTO dcr = dcrArg;
+        if (dcr == null) {
+            dcr = new DeviceCodeResponseDTO(); // put empty
+        }
+
+        DeviceCodeResponseDTO dcrEncrypted;
+        try {
+            dcrEncrypted = encryptDeviceCodeResponse(dcr);
+        } catch (GeneralSecurityException e) {
+            logger.warn("Unable to encrypt token, storing as-is", e);
+            dcrEncrypted = dcr;
+        }
+        storageFacade.put(handle, dcrEncrypted);
+    }
+
    @Override
    public void remove(String handle) {
        storageFacade.removeByHandle(handle);
@@ -181,17 +211,47 @@ public class OAuthStoreHandlerImpl implements OAuthStoreHandler {
        return encryptedAccessToken;
    }

+    private DeviceCodeResponseDTO encryptDeviceCodeResponse(DeviceCodeResponseDTO dcr) throws GeneralSecurityException {
+        DeviceCodeResponseDTO dcrEncrypted = (DeviceCodeResponseDTO) dcr.clone();
+        if (dcr.getDeviceCode() != null) {
+            dcrEncrypted.setDeviceCode(encrypt(dcr.getDeviceCode()));
+        }
+        if (dcr.getUserCode() != null) {
+            dcrEncrypted.setUserCode(encrypt(dcr.getUserCode()));
+        }
+        if (dcr.getVerificationUri() != null) {
+            dcrEncrypted.setVerificationUri(encrypt(dcr.getVerificationUri()));
+        }
+        if (dcr.getVerificationUriComplete() != null) {
+            dcrEncrypted.setVerificationUriComplete(encrypt(dcr.getVerificationUriComplete()));
+        }
+        return dcrEncrypted;
+    }
+
    private AccessTokenResponse decryptToken(AccessTokenResponse accessTokenResponse) throws GeneralSecurityException {
        AccessTokenResponse decryptedToken = (AccessTokenResponse) accessTokenResponse.clone();
        if (storageCipher.isEmpty()) {
            return decryptedToken; // do nothing if no cipher
        }
-        logger.debug("Decrypting token: {}", accessTokenResponse);
+        logger.debug("Decrypting: {}", accessTokenResponse);
        decryptedToken.setAccessToken(storageCipher.get().decrypt(accessTokenResponse.getAccessToken()));
        decryptedToken.setRefreshToken(storageCipher.get().decrypt(accessTokenResponse.getRefreshToken()));
        return decryptedToken;
    }

+    private DeviceCodeResponseDTO decryptDeviceCodeResponse(DeviceCodeResponseDTO dcr) throws GeneralSecurityException {
+        DeviceCodeResponseDTO dcrDecrypted = (DeviceCodeResponseDTO) dcr.clone();
+        if (storageCipher.isEmpty()) {
+            return dcrDecrypted; // do nothing if no cipher
+        }
+        logger.debug("Decrypting: {}", dcr);
+        dcrDecrypted.setDeviceCode(storageCipher.get().decrypt(dcr.getDeviceCode()));
+        dcrDecrypted.setUserCode(storageCipher.get().decrypt(dcr.getUserCode()));
+        dcrDecrypted.setVerificationUri(storageCipher.get().decrypt(dcr.getVerificationUri()));
+        dcrDecrypted.setVerificationUriComplete(storageCipher.get().decrypt(dcr.getVerificationUriComplete()));
+        return dcrDecrypted;
+    }
+
    private @Nullable String encrypt(String token) throws GeneralSecurityException {
        if (storageCipher.isEmpty()) {
            return token; // do nothing if no cipher
@@ -287,7 +347,7 @@ public class OAuthStoreHandlerImpl implements OAuthStoreHandler {
                if (ACCESS_TOKEN_RESPONSE.equals(recordType)) {
                    try {
                        return gson.fromJson(value, AccessTokenResponse.class);
-                    } catch (Exception e) {
+                    } catch (JsonSyntaxException e) {
                        logger.error(
                                "Unable to deserialize json, discarding AccessTokenResponse.  "
                                        + "Please check json against standard or with oauth provider. json:\n{}",
@@ -297,17 +357,27 @@ public class OAuthStoreHandlerImpl implements OAuthStoreHandler {
                } else if (SERVICE_CONFIGURATION.equals(recordType)) {
                    try {
                        return gson.fromJson(value, PersistedParams.class);
-                    } catch (Exception e) {
+                    } catch (JsonSyntaxException e) {
                        logger.error("Unable to deserialize json, discarding PersistedParams. json:\n{}", value, e);
                        return null;
                    }
                } else if (LAST_USED.equals(recordType)) {
                    try {
                        return gson.fromJson(value, Instant.class);
-                    } catch (Exception e) {
-                        logger.info("Unable to deserialize json, reset LAST_USED to now.  json:\n{}", value);
+                    } catch (JsonSyntaxException e) {
+                        logger.info("Unable to deserialize json, reset LAST_USED to now. json:\n{}", value);
                        return Instant.now();
                    }
+                } else if (DEVICE_CODE_RESPONSE.equals(recordType)) {
+                    try {
+                        return gson.fromJson(value, DeviceCodeResponseDTO.class);
+                    } catch (JsonSyntaxException e) {
+                        logger.error(
+                                "Unable to deserialize json, discarding DeviceCodeResponse. "
+                                        + "Please check json against standard or with oauth provider. json:\n{}",
+                                value, e);
+                        return null;
+                    }
                }
                return null;
            } finally {
@@ -337,6 +407,28 @@ public class OAuthStoreHandlerImpl implements OAuthStoreHandler {
            }
        }

+        public void put(String handle, @Nullable DeviceCodeResponseDTO dcr) {
+            storageLock.lock();
+            try {
+                if (dcr == null) {
+                    storage.put(DEVICE_CODE_RESPONSE.getKey(handle), (String) null);
+                } else {
+                    String gsonDcrString = gson.toJson(dcr);
+                    storage.put(DEVICE_CODE_RESPONSE.getKey(handle), gsonDcrString);
+                    String gsonDateStr = gson.toJson(Instant.now());
+                    storage.put(LAST_USED.getKey(handle), gsonDateStr);
+
+                    if (!allHandles.contains(handle)) {
+                        // update all handles index
+                        allHandles.add(handle);
+                        storage.put(STORE_KEY_INDEX_OF_HANDLES, gson.toJson(allHandles));
+                    }
+                }
+            } finally {
+                storageLock.unlock();
+            }
+        }
+
        public void put(String handle, @Nullable PersistedParams persistedParams) {
            storageLock.lock();
            try {
@@ -364,6 +456,7 @@ public class OAuthStoreHandlerImpl implements OAuthStoreHandler {
            try {
                if (allHandles.remove(handle)) { // entry exists and successfully removed
                    storage.remove(ACCESS_TOKEN_RESPONSE.getKey(handle));
+                    storage.remove(DEVICE_CODE_RESPONSE.getKey(handle));
                    storage.remove(LAST_USED.getKey(handle));
                    storage.remove(SERVICE_CONFIGURATION.getKey(handle));
                    storage.put(STORE_KEY_INDEX_OF_HANDLES, gson.toJson(allHandles)); // update all handles
@@ -19,13 +19,15 @@ import org.eclipse.jdt.annotation.Nullable;
 * Enum of types being used in the store
 *
 * @author Gary Tse - Initial contribution
+ * @author Andrew Fiddian-Green - added RFC-8628 support
 */
@NonNullByDefault
 public enum StorageRecordType {

    LAST_USED(".LastUsed"),
    ACCESS_TOKEN_RESPONSE(".AccessTokenResponse"),
-    SERVICE_CONFIGURATION(".ServiceConfiguration");
+    SERVICE_CONFIGURATION(".ServiceConfiguration"),
+    DEVICE_CODE_RESPONSE(".DeviceCodeResponse");

    private String suffix;

@@ -0,0 +1,378 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.auth.oauth2client.internal;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.*;
+import static org.mockito.Mockito.*;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+import java.time.Instant;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeoutException;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+import org.eclipse.jetty.client.HttpClient;
+import org.eclipse.jetty.client.api.ContentResponse;
+import org.eclipse.jetty.client.api.Request;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+import org.openhab.core.auth.client.oauth2.AccessTokenResponse;
+import org.openhab.core.auth.client.oauth2.DeviceCodeResponseDTO;
+import org.openhab.core.auth.client.oauth2.OAuthClientService;
+import org.openhab.core.auth.client.oauth2.OAuthException;
+import org.openhab.core.auth.client.oauth2.OAuthResponseException;
+import org.openhab.core.io.net.http.HttpClientFactory;
+import org.openhab.core.library.types.DateTimeType;
+
+import com.google.gson.FieldNamingPolicy;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSerializer;
+
+/**
+ * JUnit tests for {@link OAuthConnectorRFC8628}
+ *
+ * @author Andrew Fiddian-Green - Initial contribution
+ */
+@NonNullByDefault
+class OAuthRFC8628ClientTest {
+
+    private final Gson gson = new GsonBuilder().setDateFormat(DateTimeType.DATE_PATTERN_JSON_COMPAT)
+            .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
+            .registerTypeAdapter(Instant.class, (JsonSerializer<Instant>) (date, type,
+                    jsonSerializationContext) -> new JsonPrimitive(date.toString()))
+            .create();
+
+    /**
+     * Private wrapper class for test purposes
+     */
+    private static class OAuthConnectorRFC8628Ext extends OAuthConnectorRFC8628 {
+
+        public OAuthConnectorRFC8628Ext(OAuthClientService oAuthClientService, String handle,
+                OAuthStoreHandler oAuthStoreHandler, HttpClientFactory httpClientFactory,
+                @Nullable GsonBuilder gsonBuilder, String accessTokenRequestUrl, String deviceCodeRequestUrl,
+                String clientId, String scope) throws OAuthException {
+            super(oAuthClientService, handle, oAuthStoreHandler, httpClientFactory, gsonBuilder, accessTokenRequestUrl,
+                    deviceCodeRequestUrl, clientId, scope);
+        }
+
+        @Override
+        public void close() {
+            // this suppresses the life-cycle errors that otherwise appear in the test log
+        }
+    }
+
+    @Test
+    void testDeviceCodeResponseGoodWhenLoadedFromRemote() {
+        OAuthClientService oAuthClientService = mock(OAuthClientService.class);
+        OAuthStoreHandler oAuthStoreHandler = mock(OAuthStoreHandler.class);
+        HttpClientFactory httpClientFactory = mock(HttpClientFactory.class);
+
+        try (OAuthConnectorRFC8628 oAuthConnectorRFC8628 = new OAuthConnectorRFC8628Ext(oAuthClientService, "handle",
+                oAuthStoreHandler, httpClientFactory, null, "accessTokenRequestUrl", "deviceCodeRequestUrl", "clientId",
+                "scope")) {
+            assertNotNull(oAuthConnectorRFC8628);
+
+            Request request = mock(Request.class);
+            HttpClient httpClient = mock(HttpClient.class);
+            ContentResponse contentResponse = Mockito.mock(ContentResponse.class);
+
+            when(httpClientFactory.createHttpClient(anyString())).thenReturn(httpClient);
+            when(httpClient.isStarted()).thenReturn(true);
+
+            when(httpClient.newRequest(anyString())).thenReturn(request);
+
+            try {
+                when(request.send()).thenReturn(contentResponse);
+            } catch (InterruptedException | TimeoutException | ExecutionException e) {
+                fail(e);
+            }
+
+            DeviceCodeResponseDTO dcr = new DeviceCodeResponseDTO();
+            dcr.setDeviceCode("DeviceCode");
+            dcr.setExpiresIn(123);
+            dcr.setInterval(4L);
+            dcr.setUserCode("UserCode");
+            dcr.setVerificationUri("VerificationUri");
+            dcr.setVerificationUriComplete("VerificationUriComplete");
+
+            when(contentResponse.getStatus()).thenReturn(200);
+            when(contentResponse.getContentAsString()).thenReturn(gson.toJson(dcr), "");
+
+            DeviceCodeResponseDTO dcrOut = null;
+            try {
+                dcrOut = oAuthConnectorRFC8628.getDeviceCodeResponse();
+            } catch (OAuthException e) {
+                fail(e);
+            }
+            assertNotNull(dcrOut);
+            dcr.setCreatedOn(dcrOut.getCreatedOn()); // allow for test running time;
+
+            assertEquals(dcr, dcrOut);
+
+            verify(oAuthClientService, times(1)).isClosed();
+
+            try {
+                verify(oAuthClientService, times(1)).getAccessTokenResponse();
+            } catch (OAuthException | IOException | OAuthResponseException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthStoreHandler, times(1)).loadDeviceCodeResponse(anyString());
+            } catch (GeneralSecurityException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthClientService, times(0)).importAccessTokenResponse(any(AccessTokenResponse.class));
+                verify(oAuthClientService, times(0)).notifyAccessTokenResponse(any(AccessTokenResponse.class));
+            } catch (OAuthException e) {
+                fail(e);
+            }
+        } catch (OAuthException e) {
+            fail(e);
+        }
+    }
+
+    @Test
+    void testDeviceCodeResponseGoodWhenLoadedFromStorage() {
+        OAuthClientService oAuthClientService = mock(OAuthClientService.class);
+        OAuthStoreHandler oAuthStoreHandler = mock(OAuthStoreHandler.class);
+        HttpClientFactory httpClientFactory = mock(HttpClientFactory.class);
+
+        try (OAuthConnectorRFC8628 oAuthConnectorRFC8628 = new OAuthConnectorRFC8628Ext(oAuthClientService, "handle",
+                oAuthStoreHandler, httpClientFactory, null, "accessTokenRequestUrl", "deviceCodeRequestUrl", "clientId",
+                "scope")) {
+            assertNotNull(oAuthConnectorRFC8628);
+
+            Request request = mock(Request.class);
+            HttpClient httpClient = mock(HttpClient.class);
+            ContentResponse contentResponse = Mockito.mock(ContentResponse.class);
+
+            when(httpClientFactory.createHttpClient(anyString())).thenReturn(httpClient);
+            when(httpClient.isStarted()).thenReturn(true);
+
+            when(httpClient.newRequest(anyString())).thenReturn(request);
+
+            try {
+                when(request.send()).thenReturn(contentResponse);
+            } catch (InterruptedException | TimeoutException | ExecutionException e) {
+                fail(e);
+            }
+
+            DeviceCodeResponseDTO dcr = new DeviceCodeResponseDTO();
+            dcr.setCreatedOn(Instant.now());
+            dcr.setDeviceCode("DeviceCode");
+            dcr.setExpiresIn(123);
+            dcr.setInterval(4L);
+            dcr.setUserCode("UserCode");
+            dcr.setVerificationUri("VerificationUri");
+            dcr.setVerificationUriComplete("VerificationUriComplete");
+
+            when(contentResponse.getStatus()).thenReturn(200);
+            when(contentResponse.getContentAsString()).thenReturn("");
+
+            try {
+                when(oAuthStoreHandler.loadDeviceCodeResponse(anyString())).thenReturn(dcr);
+            } catch (GeneralSecurityException e) {
+                fail(e);
+            }
+
+            DeviceCodeResponseDTO dcrOut = null;
+            try {
+                dcrOut = oAuthConnectorRFC8628.getDeviceCodeResponse();
+            } catch (OAuthException e) {
+                fail(e);
+            }
+            assertNotNull(dcrOut);
+            dcr.setCreatedOn(dcrOut.getCreatedOn()); // allow for test running time;
+
+            assertEquals(dcr, dcrOut);
+
+            verify(oAuthClientService, times(1)).isClosed();
+
+            try {
+                verify(oAuthClientService, times(1)).getAccessTokenResponse();
+            } catch (OAuthException | IOException | OAuthResponseException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthStoreHandler, times(1)).loadDeviceCodeResponse(anyString());
+            } catch (GeneralSecurityException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthClientService, times(0)).importAccessTokenResponse(any(AccessTokenResponse.class));
+                verify(oAuthClientService, times(0)).notifyAccessTokenResponse(any(AccessTokenResponse.class));
+            } catch (OAuthException e) {
+                fail(e);
+            }
+        } catch (OAuthException e) {
+            fail(e);
+        }
+    }
+
+    @Test
+    void testDeviceCodeResponseNullWhenAccessTokenResponseLoadedFromRemote() {
+        OAuthClientService oAuthClientService = mock(OAuthClientService.class);
+        OAuthStoreHandler oAuthStoreHandler = mock(OAuthStoreHandler.class);
+        HttpClientFactory httpClientFactory = mock(HttpClientFactory.class);
+
+        try (OAuthConnectorRFC8628 oAuthConnectorRFC8628 = new OAuthConnectorRFC8628Ext(oAuthClientService, "handle",
+                oAuthStoreHandler, httpClientFactory, null, "accessTokenRequestUrl", "deviceCodeRequestUrl", "clientId",
+                "scope")) {
+            assertNotNull(oAuthConnectorRFC8628);
+
+            Request request = mock(Request.class);
+            HttpClient httpClient = mock(HttpClient.class);
+            ContentResponse contentResponse = Mockito.mock(ContentResponse.class);
+
+            when(httpClientFactory.createHttpClient(anyString())).thenReturn(httpClient);
+            when(httpClient.isStarted()).thenReturn(true);
+
+            when(httpClient.newRequest(anyString())).thenReturn(request);
+
+            try {
+                when(request.send()).thenReturn(contentResponse);
+            } catch (InterruptedException | TimeoutException | ExecutionException e) {
+                fail(e);
+            }
+
+            DeviceCodeResponseDTO dcr = new DeviceCodeResponseDTO();
+            dcr.setDeviceCode("DeviceCode");
+            dcr.setExpiresIn(123);
+            dcr.setInterval(4L);
+            dcr.setUserCode("UserCode");
+            dcr.setVerificationUri("VerificationUri");
+            dcr.setVerificationUriComplete("VerificationUriComplete");
+
+            AccessTokenResponse atr = new AccessTokenResponse();
+            atr.setAccessToken("AccessToken");
+            atr.setExpiresIn(123);
+            atr.setRefreshToken("RefreshToken");
+
+            when(contentResponse.getStatus()).thenReturn(200);
+            when(contentResponse.getContentAsString()).thenReturn(gson.toJson(dcr), gson.toJson(atr));
+
+            DeviceCodeResponseDTO dcrOut = null;
+            try {
+                dcrOut = oAuthConnectorRFC8628.getDeviceCodeResponse();
+            } catch (OAuthException e) {
+                fail(e);
+            }
+            assertNull(dcrOut);
+
+            verify(oAuthClientService, times(1)).isClosed();
+
+            try {
+                verify(oAuthClientService, times(1)).getAccessTokenResponse();
+            } catch (OAuthException | IOException | OAuthResponseException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthStoreHandler, times(1)).loadDeviceCodeResponse(anyString());
+            } catch (GeneralSecurityException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthClientService, times(1)).importAccessTokenResponse(any(AccessTokenResponse.class));
+                verify(oAuthClientService, times(1)).notifyAccessTokenResponse(any(AccessTokenResponse.class));
+            } catch (OAuthException e) {
+                fail(e);
+            }
+        } catch (OAuthException e) {
+            fail(e);
+        }
+    }
+
+    @Test
+    void testDeviceCodeResponseNullWhenAccessTokenResponseLoadedFromStorage() {
+        OAuthClientService oAuthClientService = mock(OAuthClientService.class);
+        OAuthStoreHandler oAuthStoreHandler = mock(OAuthStoreHandler.class);
+        HttpClientFactory httpClientFactory = mock(HttpClientFactory.class);
+
+        try (OAuthConnectorRFC8628 oAuthConnectorRFC8628 = new OAuthConnectorRFC8628Ext(oAuthClientService, "handle",
+                oAuthStoreHandler, httpClientFactory, null, "accessTokenRequestUrl", "deviceCodeRequestUrl", "clientId",
+                "scope")) {
+            assertNotNull(oAuthConnectorRFC8628);
+
+            AccessTokenResponse atr = new AccessTokenResponse();
+            atr.setAccessToken("AccessToken");
+            atr.setExpiresIn(123);
+            atr.setRefreshToken("RefreshToken");
+
+            try {
+                when(oAuthClientService.getAccessTokenResponse()).thenReturn(atr);
+            } catch (OAuthException | IOException | OAuthResponseException e) {
+                fail(e);
+            }
+
+            DeviceCodeResponseDTO dcr = null;
+            try {
+                dcr = oAuthConnectorRFC8628.getDeviceCodeResponse();
+            } catch (OAuthException e) {
+                fail(e);
+            }
+            assertNull(dcr);
+
+            verify(oAuthClientService, times(1)).isClosed();
+
+            try {
+                verify(oAuthClientService, times(1)).getAccessTokenResponse();
+            } catch (OAuthException | IOException | OAuthResponseException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthStoreHandler, times(0)).loadDeviceCodeResponse(anyString());
+            } catch (GeneralSecurityException e) {
+                fail(e);
+            }
+
+            try {
+                verify(oAuthClientService, times(0)).importAccessTokenResponse(any(AccessTokenResponse.class));
+                verify(oAuthClientService, times(0)).notifyAccessTokenResponse(any(AccessTokenResponse.class));
+            } catch (OAuthException e) {
+                fail(e);
+            }
+        } catch (OAuthException e) {
+            fail(e);
+        }
+    }
+
+    @Test
+    void testDeviceCodeResponseNullWhenServiceIsClosed() {
+        OAuthClientService oAuthClientService = mock(OAuthClientService.class);
+        OAuthStoreHandler oAuthStoreHandler = mock(OAuthStoreHandler.class);
+        HttpClientFactory httpClientFactory = mock(HttpClientFactory.class);
+
+        when(oAuthClientService.isClosed()).thenReturn(true);
+
+        try (OAuthConnectorRFC8628 oAuthConnectorRFC8628 = new OAuthConnectorRFC8628Ext(oAuthClientService, "handle",
+                oAuthStoreHandler, httpClientFactory, null, "accessTokenRequestUrl", "deviceCodeRequestUrl", "clientId",
+                "scope")) {
+            assertThrows(OAuthException.class, () -> oAuthConnectorRFC8628.getDeviceCodeResponse());
+        } catch (OAuthException e) {
+            fail(e);
+        }
+    }
+}
@@ -0,0 +1,154 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.auth.client.oauth2;
+
+import java.io.Serial;
+import java.io.Serializable;
+import java.time.Instant;
+import java.util.Objects;
+
+/**
+ * This {@link DeviceCodeResponseDTO} is a DTO with fields that encapsulate the data from RFC-8628 device code
+ * responses.
+ * <p>
+ * Note: RFC-8628 says 'verificationUriComplete' and 'interval' are OPTIONAL fields.
+ * <p>
+ * See {@link AccessTokenResponse} for reference.
+ *
+ * @author Andrew Fiddian-Green - Initial contribution
+ */
+public final class DeviceCodeResponseDTO implements Serializable, Cloneable {
+    /**
+     * For Serializable
+     */
+    @Serial
+    private static final long serialVersionUID = 4261783375996959200L;
+
+    private String deviceCode;
+    private long expiresIn;
+    private Long interval; // optional
+    private String userCode;
+    private String verificationUri;
+    private String verificationUriComplete; // optional
+    private Instant createdOn;
+
+    @Override
+    public Object clone() {
+        try {
+            return super.clone();
+        } catch (CloneNotSupportedException e) {
+            throw new IllegalStateException("not possible", e);
+        }
+    }
+
+    public Instant getCreatedOn() {
+        return createdOn;
+    }
+
+    public String getDeviceCode() {
+        return deviceCode;
+    }
+
+    public long getExpiresIn() {
+        return expiresIn;
+    }
+
+    public Long getInterval() {
+        return interval;
+    }
+
+    public String getUserCode() {
+        return userCode;
+    }
+
+    public String getVerificationUri() {
+        return verificationUri;
+    }
+
+    public String getVerificationUriComplete() {
+        return verificationUriComplete;
+    }
+
+    /**
+     * Calculate if the device code response is expired against the given time.
+     * It also returns true even if the response is not initialized (i.e. newly created).
+     *
+     * @param givenTime To calculate if the response is expired against the givenTime.
+     * @param tokenExpiresInBuffer A positive integer in seconds to act as additional buffer to the calculation.
+     *            This causes the response to expire earlier then the stated expiry-time given.
+     * @return true if object is not-initialized, or expired, or expired early due to buffer.
+     */
+    public boolean isExpired(Instant givenTime, int tokenExpiresInBuffer) {
+        return createdOn == null
+                || createdOn.plusSeconds(expiresIn).minusSeconds(tokenExpiresInBuffer).isBefore(givenTime);
+    }
+
+    public void setCreatedOn(Instant createdOn) {
+        this.createdOn = createdOn;
+    }
+
+    public void setDeviceCode(String deviceCode) {
+        this.deviceCode = deviceCode;
+    }
+
+    public void setExpiresIn(long expiresIn) {
+        this.expiresIn = expiresIn;
+    }
+
+    public void setInterval(Long interval) {
+        this.interval = interval;
+    }
+
+    public void setUserCode(String userCode) {
+        this.userCode = userCode;
+    }
+
+    public void setVerificationUri(String verificationUri) {
+        this.verificationUri = verificationUri;
+    }
+
+    public void setVerificationUriComplete(String verificationUriComplete) {
+        this.verificationUriComplete = verificationUriComplete;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null) {
+            return false;
+        }
+        if (getClass() != obj.getClass()) {
+            return false;
+        }
+        DeviceCodeResponseDTO other = (DeviceCodeResponseDTO) obj;
+        return Objects.equals(createdOn, other.createdOn) && Objects.equals(deviceCode, other.deviceCode)
+                && expiresIn == other.expiresIn && Objects.equals(interval, other.interval)
+                && Objects.equals(userCode, other.userCode) && Objects.equals(verificationUri, other.verificationUri)
+                && Objects.equals(verificationUriComplete, other.verificationUriComplete);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(createdOn, deviceCode, expiresIn, interval, userCode, verificationUri,
+                verificationUriComplete);
+    }
+
+    @Override
+    public String toString() {
+        return "DeviceCodeResponseDTO [deviceCode=" + deviceCode + ", expiresIn=" + expiresIn + ", interval=" + interval
+                + ", userCode=" + userCode + ", verificationUri=" + verificationUri + ", verificationUriComplete="
+                + verificationUriComplete + ", createdOn=" + createdOn + "]";
+    }
+}
@@ -309,4 +309,32 @@ public interface OAuthClientService extends AutoCloseable {
     * @return the OAuth service
     */
    OAuthClientService withGsonBuilder(GsonBuilder gsonBuilder);
+
+    /**
+     * Begins the RFC-8628 Device Code Grant Flow authentication process.
+     * Specifically it executes the following steps as described in the article in the link below:
+     *
+     * <ul>
+     * <li>Step 1: create a request and POST it to the 'device authorize url'</li>
+     * <li>Step 2: process the response and create a {@link DeviceCodeResponseDTO}</li>
+     * <li>Step 3: the user goes off to authenticate themselves at the 'user authentication url'</li>
+     * <li>Step 4: repeatedly create a request and POST it to the 'token url'</li>
+     * <li>Step 5: repeatedly read the response and eventually create a {@link AccessTokenResponse}</li>
+     * </ul>
+     *
+     * @see <a href="https://datatracker.ietf.org/doc/html/rfc8628">RFC-8628</a>
+     *
+     * @return either null or a {@link DeviceCodeResponseDTO} containing the verification uri's where
+     *         users are expected authenticate themselves
+     * @throws OAuthException
+     * @throws IOException
+     * @throws OAuthResponseException
+     */
+    @Nullable
+    DeviceCodeResponseDTO getDeviceCodeResponse() throws OAuthException;
+
+    /**
+     * Notify the service listeners about the given {@link AccessTokenResponse}.
+     */
+    void notifyAccessTokenResponse(AccessTokenResponse accessTokenResponse);
 }