Use existing sessionid on login if available

http-api/src/main/java/net/runelite/http/api/account/AccountClient.java

@@ -56,6 +56,7 @@ public class AccountClient
 		HttpUrl url = RuneLiteAPI.getApiBase().newBuilder()
 			.addPathSegment("account")
 			.addPathSegment("login")
+			.addQueryParameter("uuid", uuid.toString())
 			.build();
 
 		logger.debug("Built URI: {}", url);

http-service/src/main/java/net/runelite/http/service/account/AccountService.java

@@ -136,10 +136,8 @@ public class AccountService
 	}
 
 	@RequestMapping("/login")
-	public OAuthResponse login()
+	public OAuthResponse login(@RequestParam UUID uuid)
 	{
-		UUID uuid = UUID.randomUUID();
-
 		State state = new State();
 		state.setUuid(uuid);
 		state.setApiVersion(RuneLiteAPI.getVersion());

runelite-client/src/main/java/net/runelite/client/account/SessionManager.java

@@ -31,6 +31,7 @@ import java.io.FileWriter;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.time.Instant;
+import java.util.UUID;
 import javax.inject.Inject;
 import javax.inject.Singleton;
 import lombok.Getter;
@@ -59,7 +60,6 @@ public class SessionManager
 	private final EventBus eventBus;
 	private final ConfigManager configManager;
 	private final WSClient wsClient;
-	private final AccountClient loginClient = new AccountClient();
 
 	@Inject
 	private SessionManager(ConfigManager configManager, EventBus eventBus, WSClient wsClient)
@@ -184,6 +184,10 @@ public class SessionManager
 
 	public void login()
 	{
+		// If a session is already open, use that id. Otherwise generate a new id.
+		UUID uuid = wsClient.getSessionId() != null ? wsClient.getSessionId() : UUID.randomUUID();
+		AccountClient loginClient = new AccountClient(uuid);
+
 		final OAuthResponse login;
 
 		try

runelite-client/src/main/java/net/runelite/client/ws/WSClient.java

@@ -25,13 +25,13 @@
 package net.runelite.client.ws;
 
 import com.google.gson.Gson;
-import java.time.Duration;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Objects;
 import java.util.UUID;
 import javax.inject.Inject;
 import javax.inject.Singleton;
+import lombok.Getter;
 import lombok.extern.slf4j.Slf4j;
 import net.runelite.client.eventbus.EventBus;
 import net.runelite.http.api.RuneLiteAPI;
@@ -52,6 +52,7 @@ public class WSClient extends WebSocketListener implements AutoCloseable
 	private final Collection<Class<? extends WebsocketMessage>> messages = new HashSet<>();
 
 	private volatile Gson gson;
+	@Getter
 	private UUID sessionId;
 	private WebSocket webSocket;