client/src/main/java/envoy/client/data/ClientConfig.java

@@ -35,8 +35,6 @@ public final class ClientConfig extends Config {
 		put("server", "s", identity());
 		put("port", "p", Integer::parseInt);
 		put("localDB", "db", File::new);
-		put("user", "u", identity());
-		put("password", "pw", identity());
 	}
 
 	/**
@@ -56,28 +54,4 @@ public final class ClientConfig extends Config {
 	 * @since Envoy Client v0.1-alpha
 	 */
 	public File getLocalDB() { return (File) items.get("localDB").get(); }
-
-	/**
-	 * @return the user name
-	 * @since Envoy Client v0.3-alpha
-	 */
-	public String getUser() {
-		final String user = (String) items.get("user").get();
-		return user.equals("") ? null : user;
-	}
-
-	/**
-	 * @return the password
-	 * @since Envoy Client v0.3-alpha
-	 */
-	public String getPassword() {
-		final String password = (String) items.get("password").get();
-		return password.equals("") ? null : password;
-	}
-
-	/**
-	 * @return {@code true} if user name and password are set
-	 * @since Envoy Client v0.3-alpha
-	 */
-	public boolean hasLoginCredentials() { return getUser() != null && getPassword() != null; }
 }

client/src/main/java/envoy/client/data/LocalDB.java

@@ -8,6 +8,10 @@ import envoy.data.*;
 import envoy.event.*;
 import envoy.util.SerializationUtils;
 
+import dev.kske.eventbus.Event;
+import dev.kske.eventbus.EventBus;
+import dev.kske.eventbus.EventListener;
+
 /**
  * Stores information about the current {@link User} and their {@link Chat}s.
  * For message ID generation a {@link IDGenerator} is stored as well.
@@ -21,7 +25,7 @@ import envoy.util.SerializationUtils;
  * @author Kai S. K. Engelbart
  * @since Envoy Client v0.3-alpha
  */
-public final class LocalDB {
+public final class LocalDB implements EventListener {
 
 	private User				user;
 	private Map<String, User>	users		= new HashMap<>();
@@ -29,7 +33,8 @@ public final class LocalDB {
 	private IDGenerator			idGenerator;
 	private CacheMap			cacheMap	= new CacheMap();
 	private Instant				lastSync	= Instant.EPOCH;
-	private File				dbDir, userFile, idGeneratorFile, usersFile;
+	private String				authToken;
+	private File				dbDir, userFile, idGeneratorFile, lastLoginFile, usersFile;
 
 	/**
 	 * Constructs an empty local database. To serialize any user-specific data to
@@ -42,6 +47,7 @@ public final class LocalDB {
 	 */
 	public LocalDB(File dbDir) throws IOException {
 		this.dbDir = dbDir;
+		EventBus.getInstance().registerListener(this);
 
 		// Test if the database directory is actually a directory
 		if (dbDir.exists() && !dbDir.isDirectory())
@@ -49,6 +55,7 @@ public final class LocalDB {
 
 		// Initialize global files
 		idGeneratorFile	= new File(dbDir, "id_gen.db");
+		lastLoginFile	= new File(dbDir, "last_login.db");
 		usersFile		= new File(dbDir, "users.db");
 
 		// Initialize offline caches
@@ -76,12 +83,16 @@ public final class LocalDB {
 	 * @since Envoy Client v0.3-alpha
 	 */
 	public void save(boolean isOnline) throws IOException {
+
 		// Save users
 		SerializationUtils.write(usersFile, users);
 
 		// Save user data and last sync time stamp
 		if (user != null) SerializationUtils.write(userFile, chats, cacheMap, isOnline ? Instant.now() : lastSync);
 
+		// Save last login information
+		if (authToken != null) SerializationUtils.write(lastLoginFile, user, authToken);
+
 		// Save id generator
 		if (hasIDGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
 	}
@@ -120,6 +131,20 @@ public final class LocalDB {
 			idGenerator = SerializationUtils.read(idGeneratorFile, IDGenerator.class);
 		} catch (ClassNotFoundException | IOException e) {}
 	}
+
+	/**
+	 * Loads the last login information. Any exception thrown during this process is
+	 * ignored.
+	 *
+	 * @since Envoy Client v0.2-beta
+	 */
+	public void loadLastLogin() {
+		try (var in = new ObjectInputStream(new FileInputStream(lastLoginFile))) {
+			user		= (User) in.readObject();
+			authToken	= (String) in.readObject();
+		} catch (ClassNotFoundException | IOException e) {}
+	}
+
 	/**
 	 * Synchronizes the contact list of the client user with the chat and user
 	 * storage.
@@ -143,6 +168,11 @@ public final class LocalDB {
 			.forEach(chats::add);
 	}
 
+	@Event
+	private void onNewAuthToken(NewAuthToken evt) {
+		authToken = evt.get();
+	}
+
 	/**
 	 * @return a {@code Map<String, User>} of all users stored locally with their
 	 *         user names as keys
@@ -204,6 +234,12 @@ public final class LocalDB {
 	 */
 	public Instant getLastSync() { return lastSync; }
 
+	/**
+	 * @return the authentication token of the user
+	 * @since Envoy Client v0.2-beta
+	 */
+	public String getAuthToken() { return authToken; }
+
 	/**
 	 * Searches for a message by ID.
 	 *

client/src/main/java/envoy/client/net/Client.java

@@ -77,10 +77,12 @@ public final class Client implements EventListener, Closeable {
 		// Create object receiver
 		receiver = new Receiver(socket.getInputStream());
 
-		// Register user creation processor, contact list processor and message cache
+		// Register user creation processor, contact list processor, message cache and
+		// authentication token
 		receiver.registerProcessor(User.class, sender -> this.sender = sender);
 		receiver.registerProcessors(cacheMap.getMap());
 		receiver.registerProcessor(HandshakeRejection.class, evt -> { rejected = true; eventBus.dispatch(evt); });
+		receiver.registerProcessor(NewAuthToken.class, eventBus::dispatch);
 
 		rejected = false;
 
@@ -173,8 +175,7 @@ public final class Client implements EventListener, Closeable {
 		receiver.registerProcessor(ProfilePicChange.class, eventBus::dispatch);
 
 		// Process requests to not send any more attachments as they will not be shown
-		// to
+		// to other users
-		// other users
 		receiver.registerProcessor(NoAttachments.class, eventBus::dispatch);
 
 		// Process group creation results - they might have been disabled on the server

client/src/main/java/envoy/client/ui/Startup.java

@@ -77,27 +77,40 @@ public final class Startup extends Application {
 
 		// Prepare handshake
 		localDB.loadIDGenerator();
+		localDB.loadLastLogin();
 		context.setLocalDB(localDB);
 
+		// Configure stage
 		stage.setTitle("Envoy");
 		stage.getIcons().add(IconUtil.loadIcon("envoy_logo"));
 
+		// Create scene context
 		final var sceneContext = new SceneContext(stage);
 		context.setSceneContext(sceneContext);
 
-		// Perform automatic login if configured
+		// Authenticate with token if present
-		if (config.hasLoginCredentials())
+		if (localDB.getAuthToken() != null) {
-			performHandshake(new LoginCredentials(config.getUser(), config.getPassword(), false, Startup.VERSION, loadLastSync(config.getUser())));
+			logger.info("Attempting authentication with token...");
-		else sceneContext.load(SceneInfo.LOGIN_SCENE);
+			localDB.initializeUserStorage();
+			localDB.loadUserData();
+			if (!performHandshake(
+					LoginCredentials.loginWithToken(localDB.getUser().getName(), localDB.getAuthToken(), VERSION, localDB.getLastSync())))
+				sceneContext.load(SceneInfo.LOGIN_SCENE);
+		} else {
+
+			// Load login scene
+			sceneContext.load(SceneInfo.LOGIN_SCENE);
+		}
 	}
 
 	/**
 	 * Tries to perform a Handshake with the server.
 	 *
 	 * @param credentials the credentials to use for the handshake
+	 * @return whether the handshake was successful or offline mode could be entered
 	 * @since Envoy Client v0.2-beta
 	 */
-	public static void performHandshake(LoginCredentials credentials) {
+	public static boolean performHandshake(LoginCredentials credentials) {
 		final var cacheMap = new CacheMap();
 		cacheMap.put(Message.class, new Cache<Message>());
 		cacheMap.put(GroupMessage.class, new Cache<GroupMessage>());
@@ -109,10 +122,13 @@ public final class Startup extends Application {
 			if (client.isOnline()) {
 				loadChatScene();
 				client.initReceiver(localDB, cacheMap);
+				return true;
+			} else {
+				return false;
 			}
 		} catch (IOException | InterruptedException | TimeoutException e) {
 			logger.log(Level.INFO, "Could not connect to server. Entering offline mode...");
-			attemptOfflineMode(credentials.getIdentifier());
+			return attemptOfflineMode(credentials.getIdentifier());
 		}
 	}
 
@@ -121,9 +137,10 @@ public final class Startup extends Application {
 	 * for a given user.
 	 *
 	 * @param identifier the identifier of the user - currently his username
+	 * @return whether the offline mode could be entered
 	 * @since Envoy Client v0.2-beta
 	 */
-	public static void attemptOfflineMode(String identifier) {
+	public static boolean attemptOfflineMode(String identifier) {
 		try {
 			// Try entering offline mode
 			localDB.loadUsers();
@@ -131,10 +148,12 @@ public final class Startup extends Application {
 			if (clientUser == null) throw new EnvoyException("Could not enter offline mode: user name unknown");
 			client.setSender(clientUser);
 			loadChatScene();
+			return true;
 		} catch (final Exception e) {
 			new Alert(AlertType.ERROR, "Client error: " + e).showAndWait();
 			logger.log(Level.SEVERE, "Offline mode could not be loaded: ", e);
 			System.exit(1);
+			return false;
 		}
 	}
 

client/src/main/java/envoy/client/ui/controller/LoginScene.java

@@ -1,5 +1,6 @@
 package envoy.client.ui.controller;
 
+import java.time.Instant;
 import java.util.logging.*;
 
 import javafx.fxml.FXML;
@@ -45,6 +46,9 @@ public final class LoginScene implements EventListener {
 	@FXML
 	private Button loginButton;
 
+	@FXML
+	private CheckBox cbStaySignedIn;
+
 	@FXML
 	private Button offlineModeButton;
 
@@ -54,7 +58,7 @@ public final class LoginScene implements EventListener {
 	@FXML
 	private ImageView logo;
 
-	private boolean registration = false;
+	private boolean registration;
 
 	private static final Logger			logger	= EnvoyLog.getLogger(LoginScene.class);
 	private static final ClientConfig	config	= ClientConfig.getInstance();
@@ -74,16 +78,21 @@ public final class LoginScene implements EventListener {
 
 	@FXML
 	private void loginButtonPressed() {
+		final String user = userTextField.getText(), pass = passwordField.getText(), repeatPass = repeatPasswordField.getText();
+		final boolean	requestToken	= cbStaySignedIn.isSelected();
 
 		// Prevent registration with unequal passwords
-		if (registration && !passwordField.getText().equals(repeatPasswordField.getText())) {
+		if (registration && !pass.equals(repeatPass)) {
 			new Alert(AlertType.ERROR, "The entered password is unequal to the repeated one").showAndWait();
 			repeatPasswordField.clear();
-		} else if (!Bounds.isValidContactName(userTextField.getText())) {
+		} else if (!Bounds.isValidContactName(user)) {
 			new Alert(AlertType.ERROR, "The entered user name is not valid (" + Bounds.CONTACT_NAME_PATTERN + ")").showAndWait();
 			userTextField.clear();
-		} else Startup.performHandshake(new LoginCredentials(userTextField.getText(), passwordField.getText(), registration, Startup.VERSION,
+		} else {
-				Startup.loadLastSync(userTextField.getText())));
+			Instant lastSync = Startup.loadLastSync(userTextField.getText());
+			Startup.performHandshake(registration ? LoginCredentials.registration(user, pass, requestToken, Startup.VERSION, lastSync)
+					: LoginCredentials.login(user, pass, requestToken, Startup.VERSION, lastSync));
+		}
 	}
 
 	@FXML

client/src/main/java/module-info.java

@@ -23,4 +23,5 @@ module envoy.client {
 	opens envoy.client.ui.custom to javafx.graphics, javafx.fxml;
 	opens envoy.client.ui.settings to envoy.client.util;
 	opens envoy.client.net to dev.kske.eventbus;
+	opens envoy.client.data to dev.kske.eventbus;
 }

client/src/main/resources/fxml/LoginScene.fxml

@@ -2,6 +2,7 @@
 
 <?import javafx.geometry.Insets?>
 <?import javafx.scene.control.Button?>
+<?import javafx.scene.control.CheckBox?>
 <?import javafx.scene.control.Label?>
 <?import javafx.scene.control.PasswordField?>
 <?import javafx.scene.control.TextField?>
@@ -32,9 +33,7 @@
             <Insets bottom="5.0" left="5.0" right="5.0" top="5.0" />
          </padding>
       </Label>
-		<Label alignment="TOP_CENTER" contentDisplay="CENTER"
+		<Label alignment="TOP_CENTER" contentDisplay="CENTER" prefHeight="33.0" prefWidth="110.0" text="LOGIN" textAlignment="CENTER">
-			prefHeight="33.0" prefWidth="110.0" text="LOGIN"
-			textAlignment="CENTER">
 			<font>
 				<Font size="26.0" />
 			</font>
@@ -92,6 +91,11 @@
             <Insets bottom="2.0" left="125.0" right="125.0" top="2.0" />
          </padding>
 				</Button>
+      <CheckBox fx:id="cbStaySignedIn" mnemonicParsing="false" text="Keep me signed in">
+         <VBox.margin>
+            <Insets bottom="10.0" top="10.0" />
+         </VBox.margin>
+      </CheckBox>
       <HBox alignment="CENTER" prefHeight="30.0" prefWidth="200.0">
          <children>
             <Label fx:id="registerTextLabel" text="No account yet?" />

common/src/main/java/envoy/data/LoginCredentials.java

@@ -7,6 +7,9 @@ import java.time.Instant;
  * Contains a {@link User}'s login / registration information as well as the
  * client version.
  * <p>
+ * If the authentication is performed with a token, the token is stored instead
+ * of the password.
+ * <p>
  * Project: <strong>envoy-common</strong><br>
  * File: <strong>LoginCredentials.java</strong><br>
  * Created: <strong>29.12.2019</strong><br>
@@ -17,35 +20,73 @@ import java.time.Instant;
 public final class LoginCredentials implements Serializable {
 
 	private final String	identifier, password, clientVersion;
-	private final boolean	registration;
+	private final boolean	registration, token, requestToken;
 	private final Instant	lastSync;
 
-	private static final long serialVersionUID = 3;
+	private static final long serialVersionUID = 4;
 
-	/**
+	private LoginCredentials(String identifier, String password, boolean registration, boolean token, boolean requestToken, String clientVersion,
-	 * Initializes login credentials for a handshake.
+			Instant lastSync) {
-	 *
-	 * @param identifier    the identifier of the user
-	 * @param password      the password of the user
-	 * @param registration  signifies that these credentials are used for user
-	 *                      registration instead of user login
-	 * @param clientVersion the version of the client sending these credentials
-	 * @param lastSync      the time stamp of the last synchronization
-	 * @since Envoy Common v0.2-beta
-	 */
-	public LoginCredentials(String identifier, String password, boolean registration, String clientVersion, Instant lastSync) {
 		this.identifier		= identifier;
 		this.password		= password;
 		this.registration	= registration;
+		this.token			= token;
+		this.requestToken	= requestToken;
 		this.clientVersion	= clientVersion;
 		this.lastSync		= lastSync;
 	}
 
+	/**
+	 * Creates login credentials for a regular login.
+	 *
+	 * @param identifier    the identifier of the user
+	 * @param password      the password of the user
+	 * @param requestToken  requests the server to generate an authentication token
+	 * @param clientVersion the version of the client sending these credentials
+	 * @param lastSync      the timestamp of the last synchronization
+	 * @return the created login credentials
+	 * @since Envoy Common v0.2-beta
+	 */
+	public static LoginCredentials login(String identifier, String password, boolean requestToken, String clientVersion, Instant lastSync) {
+		return new LoginCredentials(identifier, password, false, false, requestToken, clientVersion, lastSync);
+	}
+
+	/**
+	 * Creates login credentials for a login with an authentication token.
+	 *
+	 * @param identifier    the identifier of the user
+	 * @param token         the authentication token of the user
+	 * @param clientVersion the version of the client sending these credentials
+	 * @param lastSync      the timestamp of the last synchronization
+	 * @return the created login credentials
+	 * @since Envoy Common v0.2-beta
+	 */
+	public static LoginCredentials loginWithToken(String identifier, String token, String clientVersion, Instant lastSync) {
+		return new LoginCredentials(identifier, token, false, true, false, clientVersion, lastSync);
+	}
+
+	/**
+	 * Creates login credentials for a registration.
+	 *
+	 * @param identifier    the identifier of the user
+	 * @param password      the password of the user
+	 * @param requestToken  requests the server to generate an authentication token
+	 * @param clientVersion the version of the client sending these credentials
+	 * @param lastSync      the timestamp of the last synchronization
+	 * @return the created login credentials
+	 * @since Envoy Common v0.2-beta
+	 */
+	public static LoginCredentials registration(String identifier, String password, boolean requestToken, String clientVersion, Instant lastSync) {
+		return new LoginCredentials(identifier, password, true, false, requestToken, clientVersion, lastSync);
+	}
+
 	@Override
 	public String toString() {
-		return String.format("LoginCredentials[identifier=%s,registration=%b,clientVersion=%s,lastSync=%s]",
+		return String.format("LoginCredentials[identifier=%s,registration=%b,token=%b,requestToken=%b,clientVersion=%s,lastSync=%s]",
 				identifier,
 				registration,
+				token,
+				requestToken,
 				clientVersion,
 				lastSync);
 	}
@@ -69,6 +110,19 @@ public final class LoginCredentials implements Serializable {
 	 */
 	public boolean isRegistration() { return registration; }
 
+	/**
+	 * @return {@code true} if these credentials use an authentication token instead
+	 *         of a password
+	 * @since Envoy Common v0.2-beta
+	 */
+	public boolean usesToken() { return token; }
+
+	/**
+	 * @return {@code true} if the server should generate a new authentication token
+	 * @since Envoy Common v0.2-beta
+	 */
+	public boolean requestToken() { return requestToken; }
+
 	/**
 	 * @return the version of the client sending these credentials
 	 * @since Envoy Common v0.1-beta
@@ -76,7 +130,7 @@ public final class LoginCredentials implements Serializable {
 	public String getClientVersion() { return clientVersion; }
 
 	/**
-	 * @return the time stamp of the last synchronization
+	 * @return the timestamp of the last synchronization
 	 * @since Envoy Common v0.2-beta
 	 */
 	public Instant getLastSync() { return lastSync; }

common/src/main/java/envoy/event/HandshakeRejection.java

@@ -35,6 +35,13 @@ public final class HandshakeRejection extends Event<String> {
 	 */
 	public static final String WRONG_VERSION = "Incompatible client version";
 
+	/**
+	 * Select this value if the client provided an invalid authentication token.
+	 *
+	 * @since Envoy Common v0.2-beta
+	 */
+	public static final String INVALID_TOKEN = "Invalid authentication token";
+
 	/**
 	 * Select this value if the handshake could not be completed for some different
 	 * reason.

common/src/main/java/envoy/event/NewAuthToken.java

@@ -0,0 +1,29 @@
+package envoy.event;
+
+/**
+ * This event can be used to transmit a new authentication token to a client.
+ * <p>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>NewAuthToken.java</strong><br>
+ * Created: <strong>19.09.2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Common v0.2-beta
+ */
+public class NewAuthToken extends Event<String> {
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * Constructs a new authentication token event.
+	 *
+	 * @param token the token to transmit
+	 * @since Envoy Common v0.2-beta
+	 */
+	public NewAuthToken(String token) {
+		super(token);
+	}
+
+	@Override
+	public String toString() { return "NewAuthToken"; }
+}

server/src/main/java/envoy/server/data/ServerConfig.java

@@ -35,6 +35,8 @@ public final class ServerConfig extends Config {
 		put("enableIssueReporting", "e-ir", Boolean::parseBoolean);
 		put("enableGroups", "e-g", Boolean::parseBoolean);
 		put("enableAttachments", "e-a", Boolean::parseBoolean);
+		// user authentication
+		put("authTokenExpiration", "tok-exp", Integer::parseInt);
 	}
 
 	/**
@@ -93,4 +95,10 @@ public final class ServerConfig extends Config {
 	 * @since Envoy Server v0.2-beta
 	 */
 	public String getIssueAuthToken() { return (String) items.get("issueAuthToken").get(); }
+
+	/**
+	 * @return the amount of days after which user authentication tokens expire
+	 * @since Envoy Server v0.2-beta
+	 */
+	public Integer getAuthTokenExpiration() { return (Integer) items.get("authTokenExpiration").get(); }
 }

server/src/main/java/envoy/server/data/User.java

@@ -65,6 +65,12 @@ public final class User extends Contact {
 	@Column(name = "password_hash")
 	private String passwordHash;
 
+	@Column(name = "auth_token")
+	private String authToken;
+
+	@Column(name = "auth_token_expiration")
+	private Instant authTokenExpiration;
+
 	@Column(name = "last_seen")
 	private Instant lastSeen;
 
@@ -90,6 +96,31 @@ public final class User extends Contact {
 	 */
 	public void setPasswordHash(String passwordHash) { this.passwordHash = passwordHash; }
 
+	/**
+	 * @return the authentication token
+	 * @since Envoy Server v0.2-beta
+	 */
+	public String getAuthToken() { return authToken; }
+
+	/**
+	 * @param authToken the authentication token to set
+	 * @since Envoy Server v0.2-beta
+	 */
+	public void setAuthToken(String authToken) { this.authToken = authToken; }
+
+	/**
+	 * @return the time at which the authentication token expires
+	 * @since Envoy Server v0.2-beta
+	 */
+	public Instant getAuthTokenExpiration() { return authTokenExpiration; }
+
+	/**
+	 * @param authTokenExpiration the authentication token expiration timestamp to
+	 *                            set
+	 * @since Envoy Server v0.2-beta
+	 */
+	public void setAuthTokenExpiration(Instant authTokenExpiration) { this.authTokenExpiration = authTokenExpiration; }
+
 	/**
 	 * @return the last date the user has been online
 	 * @since Envoy Server Standalone v0.2-beta

server/src/main/java/envoy/server/processors/LoginCredentialProcessor.java

@@ -5,26 +5,18 @@ import static envoy.data.User.UserStatus.ONLINE;
 import static envoy.event.HandshakeRejection.*;
 
 import java.time.Instant;
-import java.util.Collections;
+import java.time.temporal.ChronoUnit;
-import java.util.HashSet;
+import java.util.*;
-import java.util.List;
 import java.util.logging.Logger;
 
 import javax.persistence.NoResultException;
 
 import envoy.data.LoginCredentials;
-import envoy.event.GroupMessageStatusChange;
+import envoy.event.*;
-import envoy.event.HandshakeRejection;
+import envoy.server.data.*;
-import envoy.event.MessageStatusChange;
+import envoy.server.net.*;
-import envoy.server.data.GroupMessage;
+import envoy.server.util.*;
-import envoy.server.data.PersistenceManager;
+import envoy.util.*;
-import envoy.server.data.User;
-import envoy.server.net.ConnectionManager;
-import envoy.server.net.ObjectWriteProxy;
-import envoy.server.util.PasswordUtil;
-import envoy.server.util.VersionUtil;
-import envoy.util.Bounds;
-import envoy.util.EnvoyLog;
 
 /**
  * This {@link ObjectProcessor} handles {@link LoginCredentials}.<br>
@@ -62,24 +54,39 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 			try {
 				user = persistenceManager.getUserByName(credentials.getIdentifier());
 
-				// Checking if user is already online
+				// Check if the user is already online
 				if (connectionManager.isOnline(user.getID())) {
 					logger.warning(user + " is already online!");
 					writeProxy.write(socketID, new HandshakeRejection(INTERNAL_ERROR));
 					return;
 				}
-				// Evaluating the correctness of the password hash
+
+				// Authenticate with password or token
+				if (credentials.usesToken()) {
+
+					// Check the token
+					if (user.getAuthToken() == null || user.getAuthTokenExpiration().isBefore(Instant.now())
+							|| !user.getAuthToken().equals(credentials.getPassword())) {
+						logger.info(user + " tried to use an invalid token.");
+						writeProxy.write(socketID, new HandshakeRejection(INVALID_TOKEN));
+						return;
+					}
+				} else {
+
+					// Check the password hash
 					if (!PasswordUtil.validate(credentials.getPassword(), user.getPasswordHash())) {
 						logger.info(user + " has entered the wrong password.");
 						writeProxy.write(socketID, new HandshakeRejection(WRONG_PASSWORD_OR_USER));
 						return;
 					}
+				}
 			} catch (NoResultException e) {
 				logger.info("The requested user does not exist.");
 				writeProxy.write(socketID, new HandshakeRejection(WRONG_PASSWORD_OR_USER));
 				return;
 			}
 		} else {
+
 			// Validate user name
 			if (!Bounds.isValidContactName(credentials.getIdentifier())) {
 				logger.info("The requested user name is not valid.");
@@ -87,7 +94,8 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 				return;
 			}
 			try {
-				// Checking that no user already has this identifier
+
+				// Check if the name is taken
 				PersistenceManager.getInstance().getUserByName(credentials.getIdentifier());
 
 				// This code only gets executed if this user already exists
@@ -114,6 +122,25 @@ public final class LoginCredentialProcessor implements ObjectProcessor<LoginCred
 		user.setStatus(ONLINE);
 		UserStatusChangeProcessor.updateUserStatus(user);
 
+		// Process token request
+		if (credentials.requestToken()) {
+			String token;
+
+			if (user.getAuthToken() != null && user.getAuthTokenExpiration().isAfter(Instant.now())) {
+
+				// Reuse existing token and delay expiration date
+				token = user.getAuthToken();
+			} else {
+
+				// Generate new token
+				token = AuthTokenGenerator.nextToken();
+				user.setAuthToken(token);
+			}
+			user.setAuthTokenExpiration(Instant.now().plus(ServerConfig.getInstance().getAuthTokenExpiration().longValue(), ChronoUnit.DAYS));
+			persistenceManager.updateContact(user);
+			writeProxy.write(socketID, new NewAuthToken(token));
+		}
+
 		final var pendingMessages = PersistenceManager.getInstance().getPendingMessages(user, credentials.getLastSync());
 		pendingMessages.removeIf(GroupMessage.class::isInstance);
 		logger.fine("Sending " + pendingMessages.size() + " pending messages to " + user + "...");

server/src/main/java/envoy/server/util/AuthTokenGenerator.java

@@ -0,0 +1,35 @@
+package envoy.server.util;
+
+import java.security.SecureRandom;
+
+/**
+ * Provides a secure token generation algorithm.
+ * <p>
+ * Project: <strong>envoy-server</strong><br>
+ * File: <strong>AuthTokenGenerator.java</strong><br>
+ * Created: <strong>19.09.2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy Server v0.2-beta
+ */
+public final class AuthTokenGenerator {
+
+	private static final int			TOKEN_LENGTH	= 128;
+	private static final char[]			CHARACTERS		= "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
+	private static final char[]			BUFF			= new char[TOKEN_LENGTH];
+	private static final SecureRandom	RANDOM			= new SecureRandom();
+
+	private AuthTokenGenerator() {}
+
+	/**
+	 * Generates a random authentication token.
+	 *
+	 * @return a random authentication token
+	 * @since Envoy Server v0.2-beta
+	 */
+	public static String nextToken() {
+		for (int i = 0; i < BUFF.length; ++i)
+			BUFF[i] = CHARACTERS[RANDOM.nextInt(CHARACTERS.length)];
+		return new String(BUFF);
+	}
+}

server/src/main/resources/server.properties

@@ -10,3 +10,4 @@ featureLabel=119
 issueAuthToken=
 consoleLevelBarrier=FINEST
 fileLevelBarrier=WARNING
+authTokenExpiration=90