diff --git a/back/src/Controller/AuthenticateController.ts b/back/src/Controller/AuthenticateController.ts
index 6eaa14ca..db5fb1ce 100644
--- a/back/src/Controller/AuthenticateController.ts
+++ b/back/src/Controller/AuthenticateController.ts
@@ -4,7 +4,7 @@ import {BAD_REQUEST, OK} from "http-status-codes";
 import {SECRET_KEY, URL_ROOM_STARTED} from "../Enum/EnvironmentVariable"; //TODO fix import by "_Enum/..."
 import { uuid } from 'uuidv4';
 
-export class AuthenticateController{
+export class AuthenticateController {
     App : Application;
 
     constructor(App : Application) {
@@ -14,7 +14,8 @@ export class AuthenticateController{
 
     //permit to login on application. Return token to connect on Websocket IO.
     login(){
-        this.App.post("/login", (req: Request, res: Response) => {
+        // For now, let's completely forget the /login route.
+        /*this.App.post("/login", (req: Request, res: Response) => {
             let param = req.body;
             if(!param.email){
                 return res.status(BAD_REQUEST).send({
@@ -29,6 +30,6 @@ export class AuthenticateController{
                 mapUrlStart: URL_ROOM_STARTED,
                 userId: userId,
             });
-        });
+        });*/
     }
-}
\ No newline at end of file
+}
diff --git a/back/src/Controller/IoSocketController.ts b/back/src/Controller/IoSocketController.ts
index d3410a13..6349b352 100644
--- a/back/src/Controller/IoSocketController.ts
+++ b/back/src/Controller/IoSocketController.ts
@@ -14,6 +14,7 @@ import {UserInterface} from "_Model/UserInterface";
 enum SockerIoEvent {
     CONNECTION = "connection",
     DISCONNECT = "disconnect",
+    ATTRIBUTE_USER_ID = "attribute-user-id", // Sent from server to client just after the connexion is established to give the client its unique id.
     JOIN_ROOM = "join-room",
     USER_POSITION = "user-position",
     WEBRTC_SIGNAL = "webrtc-signal",
@@ -33,7 +34,8 @@ export class IoSocketController {
         this.Io = socketIO(server);
 
         // Authentication with token. it will be decoded and stored in the socket.
-        this.Io.use((socket: Socket, next) => {
+        // Completely commented for now, as we do not use the "/login" route at all.
+        /*this.Io.use((socket: Socket, next) => {
             if (!socket.handshake.query || !socket.handshake.query.token) {
                 return next(new Error('Authentication error'));
             }
@@ -47,7 +49,7 @@ export class IoSocketController {
                 (socket as ExSocketInterface).token = tokenDecoded;
                 next();
             });
-        });
+        });*/
 
         this.ioConnection();
         this.shareUsersPosition();
@@ -74,6 +76,7 @@ export class IoSocketController {
         let userId = lastUser.id;
         let client: ExSocketInterface|null = this.searchClientById(userId);
         if (client === null) {
+            console.warn('Could not find client ', userId, ' in group')
             return;
         }
         let roomId = client.roomId;
@@ -180,7 +183,6 @@ export class IoSocketController {
                     socket.leave(Client.webRtcRoomId);
 
                     //delete all socket information
-                    delete Client.userId;
                     delete Client.webRtcRoomId;
                     delete Client.roomId;
                     delete Client.token;
@@ -190,6 +192,9 @@ export class IoSocketController {
                     console.error(e);
                 }
             });
+
+            // Let's send the user id to the user
+            socket.emit(SockerIoEvent.ATTRIBUTE_USER_ID, socket.id);
         });
     }
 
@@ -201,11 +206,12 @@ export class IoSocketController {
         let clients: Array<any> = Object.values(this.Io.sockets.sockets);
         for (let i = 0; i < clients.length; i++) {
             let client: ExSocketInterface = clients[i];
-            if (client.userId !== userId) {
-                continue
+            if (client.id !== userId) {
+                continue;
             }
             return client;
         }
+        console.log("Could not find user with id ", userId);
         return null;
     }
 
@@ -216,7 +222,7 @@ export class IoSocketController {
         let clients: Array<any> = Object.values(this.Io.sockets.sockets);
         for (let i = 0; i < clients.length; i++) {
             let client: ExSocketInterface = clients[i];
-            if (client.userId !== userId) {
+            if (client.id !== userId) {
                 continue
             }
             return client;
@@ -230,7 +236,7 @@ export class IoSocketController {
      */
     sendDisconnectedEvent(Client: ExSocketInterface) {
         Client.broadcast.emit(SockerIoEvent.WEBRTC_DISCONNECT, JSON.stringify({
-            userId: Client.userId
+            userId: Client.id
         }));
 
         //disconnect webrtc room
@@ -248,14 +254,16 @@ export class IoSocketController {
     leaveRoom(Client : ExSocketInterface){
         //lease previous room and world
         if(Client.roomId){
-            //user leave previous room
-            Client.leave(Client.roomId);
             //user leave previous world
             let world : World|undefined = this.Worlds.get(Client.roomId);
             if(world){
+                console.log('Entering world.leave')
                 world.leave(Client);
-                this.Worlds.set(Client.roomId, world);
+                //this.Worlds.set(Client.roomId, world);
             }
+            //user leave previous room
+            Client.leave(Client.roomId);
+            delete Client.roomId;
         }
     }
     /**
@@ -293,7 +301,7 @@ export class IoSocketController {
                 });
             });
             //join world
-            world.join(messageUserPosition);
+            world.join(Client, messageUserPosition);
             this.Worlds.set(messageUserPosition.roomId, world);
         }
 
@@ -322,11 +330,11 @@ export class IoSocketController {
         clients.forEach((client: ExSocketInterface, index: number) => {
 
             let clientsId = clients.reduce((tabs: Array<any>, clientId: ExSocketInterface, indexClientId: number) => {
-                if (!clientId.userId || clientId.userId === client.userId) {
+                if (!clientId.id || clientId.id === client.id) {
                     return tabs;
                 }
                 tabs.push({
-                    userId: clientId.userId,
+                    userId: clientId.id,
                     name: clientId.name,
                     initiator: index <= indexClientId
                 });
@@ -341,7 +349,7 @@ export class IoSocketController {
     saveUserInformation(socket: ExSocketInterface, message: MessageUserPosition) {
         socket.position = message.position;
         socket.roomId = message.roomId;
-        socket.userId = message.userId;
+        //socket.userId = message.userId;
         socket.name = message.name;
         socket.character = message.character;
     }
@@ -354,9 +362,9 @@ export class IoSocketController {
         }
         rooms.refreshUserPosition(rooms, this.Io);
 
-        // update position in the worl
+        // update position in the world
         let data = {
-            userId: Client.userId,
+            userId: Client.id,
             roomId: Client.roomId,
             position: Client.position,
             name: Client.name,
@@ -367,7 +375,7 @@ export class IoSocketController {
         if (!world) {
             return;
         }
-        world.updatePosition(messageUserPosition);
+        world.updatePosition(Client, messageUserPosition);
         this.Worlds.set(messageUserPosition.roomId, world);
     }
 
diff --git a/back/src/Model/Websocket/ExSocketInterface.ts b/back/src/Model/Websocket/ExSocketInterface.ts
index 22cd29c2..c55a9759 100644
--- a/back/src/Model/Websocket/ExSocketInterface.ts
+++ b/back/src/Model/Websocket/ExSocketInterface.ts
@@ -1,11 +1,12 @@
 import {Socket} from "socket.io";
 import {PointInterface} from "./PointInterface";
+import {Identificable} from "./Identificable";
 
-export interface ExSocketInterface extends Socket {
+export interface ExSocketInterface extends Socket, Identificable {
     token: any;
     roomId: string;
     webRtcRoomId: string;
-    userId: string;
+    //userId: string;
     name: string;
     character: string;
     position: PointInterface;
diff --git a/back/src/Model/Websocket/ExtRooms.ts b/back/src/Model/Websocket/ExtRooms.ts
index 7fb6216d..43395a28 100644
--- a/back/src/Model/Websocket/ExtRooms.ts
+++ b/back/src/Model/Websocket/ExtRooms.ts
@@ -22,7 +22,7 @@ let RefreshUserPositionFunction = function(rooms : ExtRooms, Io: socketIO.Server
             continue;
         }
         let data = {
-            userId: socket.userId,
+            userId: socket.id,
             roomId: socket.roomId,
             position: socket.position,
             name: socket.name,
diff --git a/back/src/Model/Websocket/Identificable.ts b/back/src/Model/Websocket/Identificable.ts
new file mode 100644
index 00000000..8c344259
--- /dev/null
+++ b/back/src/Model/Websocket/Identificable.ts
@@ -0,0 +1,3 @@
+export interface Identificable {
+    id: string;
+}
diff --git a/back/src/Model/Websocket/Message.ts b/back/src/Model/Websocket/Message.ts
index ccf5d287..f4bdead8 100644
--- a/back/src/Model/Websocket/Message.ts
+++ b/back/src/Model/Websocket/Message.ts
@@ -16,6 +16,7 @@ export class Message {
     }
 
     toJson() {
+
         return {
             userId: this.userId,
             roomId: this.roomId,
diff --git a/back/src/Model/World.ts b/back/src/Model/World.ts
index 72bf029c..19e8c194 100644
--- a/back/src/Model/World.ts
+++ b/back/src/Model/World.ts
@@ -5,6 +5,7 @@ import {Distance} from "./Distance";
 import {UserInterface} from "./UserInterface";
 import {ExSocketInterface} from "_Model/Websocket/ExSocketInterface";
 import {PositionInterface} from "_Model/PositionInterface";
+import {Identificable} from "_Model/Websocket/Identificable";
 
 export type ConnectCallback = (user: string, group: Group) => void;
 export type DisconnectCallback = (user: string, group: Group) => void;
@@ -14,17 +15,17 @@ export type GroupUpdatedCallback = (group: Group) => void;
 export type GroupDeletedCallback = (uuid: string, lastUser: UserInterface) => void;
 
 export class World {
-    private minDistance: number;
-    private groupRadius: number;
+    private readonly minDistance: number;
+    private readonly groupRadius: number;
 
     // Users, sorted by ID
-    private users: Map<string, UserInterface>;
-    private groups: Group[];
+    private readonly users: Map<string, UserInterface>;
+    private readonly groups: Group[];
 
-    private connectCallback: ConnectCallback;
-    private disconnectCallback: DisconnectCallback;
-    private groupUpdatedCallback: GroupUpdatedCallback;
-    private groupDeletedCallback: GroupDeletedCallback;
+    private readonly connectCallback: ConnectCallback;
+    private readonly disconnectCallback: DisconnectCallback;
+    private readonly groupUpdatedCallback: GroupUpdatedCallback;
+    private readonly groupDeletedCallback: GroupDeletedCallback;
 
     constructor(connectCallback: ConnectCallback,
                 disconnectCallback: DisconnectCallback,
@@ -47,25 +48,29 @@ export class World {
         return this.groups;
     }
 
-    public join(userPosition: MessageUserPosition): void {
-        this.users.set(userPosition.userId, {
-            id: userPosition.userId,
+    public join(socket : Identificable, userPosition: MessageUserPosition): void {
+        this.users.set(socket.id, {
+            id: socket.id,
             position: userPosition.position
         });
         // Let's call update position to trigger the join / leave room
-        this.updatePosition(userPosition);
+        this.updatePosition(socket, userPosition);
     }
 
-    public leave(user : ExSocketInterface){
+    public leave(user : Identificable){
         let userObj = this.users.get(user.id);
-        if (userObj !== undefined && typeof userObj.group !== 'undefined') {
-            this.leaveGroup(user);
+        if (userObj === undefined) {
+            // FIXME: this seems always wrong. I guess user.id is different from userPosition.userId
+            console.warn('User ', user.id, 'does not belong to world! It should!');
         }
-        this.users.delete(user.userId);
+        if (userObj !== undefined && typeof userObj.group !== 'undefined') {
+            this.leaveGroup(userObj);
+        }
+        this.users.delete(user.id);
     }
 
-    public updatePosition(userPosition: MessageUserPosition): void {
-        let user = this.users.get(userPosition.userId);
+    public updatePosition(socket : Identificable, userPosition: MessageUserPosition): void {
+        let user = this.users.get(socket.id);
         if(typeof user === 'undefined') {
             return;
         }
@@ -118,7 +123,6 @@ export class World {
             throw new Error("The user is part of no group");
         }
         group.leave(user);
-
         if (group.isEmpty()) {
             this.groupDeletedCallback(group.getId(), user);
             group.destroy();
diff --git a/back/tests/WorldTest.ts b/back/tests/WorldTest.ts
index 57f0f3f4..148e7383 100644
--- a/back/tests/WorldTest.ts
+++ b/back/tests/WorldTest.ts
@@ -17,36 +17,36 @@ describe("World", () => {
 
         let world = new World(connect, disconnect, 160, 160, () => {}, () => {});
 
-        world.join(new MessageUserPosition({
-            userId: "foo",
+        world.join({ id: "foo" }, new MessageUserPosition({
+            userId: "foofoo",
             roomId: 1,
             position: new Point(100, 100)
         }));
 
-        world.join(new MessageUserPosition({
-            userId: "bar",
+        world.join({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(500, 100)
         }));
 
-        world.updatePosition(new MessageUserPosition({
-            userId: "bar",
+        world.updatePosition({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(261, 100)
         }));
 
         expect(connectCalledNumber).toBe(0);
 
-        world.updatePosition(new MessageUserPosition({
-            userId: "bar",
+        world.updatePosition({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(101, 100)
         }));
 
         expect(connectCalledNumber).toBe(2);
 
-        world.updatePosition(new MessageUserPosition({
-            userId: "bar",
+        world.updatePosition({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(102, 100)
         }));
@@ -64,14 +64,14 @@ describe("World", () => {
 
         let world = new World(connect, disconnect, 160, 160, () => {}, () => {});
 
-        world.join(new MessageUserPosition({
-            userId: "foo",
+        world.join({ id: "foo" }, new MessageUserPosition({
+            userId: "foofoo",
             roomId: 1,
             position: new Point(100, 100)
         }));
 
-        world.join(new MessageUserPosition({
-            userId: "bar",
+        world.join({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(200, 100)
         }));
@@ -80,16 +80,16 @@ describe("World", () => {
         connectCalled = false;
 
         // baz joins at the outer limit of the group
-        world.join(new MessageUserPosition({
-            userId: "baz",
+        world.join({ id: "baz" }, new MessageUserPosition({
+            userId: "bazbaz",
             roomId: 1,
             position: new Point(311, 100)
         }));
 
         expect(connectCalled).toBe(false);
 
-        world.updatePosition(new MessageUserPosition({
-            userId: "baz",
+        world.updatePosition({ id: "baz" }, new MessageUserPosition({
+            userId: "bazbaz",
             roomId: 1,
             position: new Point(309, 100)
         }));
@@ -109,14 +109,14 @@ describe("World", () => {
 
         let world = new World(connect, disconnect, 160, 160, () => {}, () => {});
 
-        world.join(new MessageUserPosition({
-            userId: "foo",
+        world.join({ id: "foo" }, new MessageUserPosition({
+            userId: "foofoo",
             roomId: 1,
             position: new Point(100, 100)
         }));
 
-        world.join(new MessageUserPosition({
-            userId: "bar",
+        world.join({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(259, 100)
         }));
@@ -124,16 +124,16 @@ describe("World", () => {
         expect(connectCalled).toBe(true);
         expect(disconnectCallNumber).toBe(0);
 
-        world.updatePosition(new MessageUserPosition({
-            userId: "bar",
+        world.updatePosition({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(100+160+160+1, 100)
         }));
 
         expect(disconnectCallNumber).toBe(2);
 
-        world.updatePosition(new MessageUserPosition({
-            userId: "bar",
+        world.updatePosition({ id: "bar" }, new MessageUserPosition({
+            userId: "barbar",
             roomId: 1,
             position: new Point(262, 100)
         }));
diff --git a/front/src/Connexion.ts b/front/src/Connexion.ts
index d6d37025..f29bef2e 100644
--- a/front/src/Connexion.ts
+++ b/front/src/Connexion.ts
@@ -18,7 +18,8 @@ enum EventMessage{
     GROUP_DELETE = "group-delete",
 
     CONNECT_ERROR = "connect_error",
-    RECONNECT = "reconnect"
+    RECONNECT = "reconnect",
+    ATTRIBUTE_USER_ID = "attribute-user-id" // Sent from server to client just after the connexion is established to give the client its unique id.
 }
 
 class Message {
@@ -184,25 +185,37 @@ export class Connexion implements ConnexionInterface {
      * @param characterSelected
      */
     createConnexion(characterSelected: string): Promise<ConnexionInterface> {
-        return Axios.post(`${API_URL}/login`, {email: this.email})
+        /*return Axios.post(`${API_URL}/login`, {email: this.email})
             .then((res) => {
                 this.token = res.data.token;
-                this.userId = res.data.userId;
+                this.userId = res.data.userId;*/
 
                 this.socket = SocketIo(`${API_URL}`, {
-                    query: {
+                    /*query: {
                         token: this.token
-                    }
+                    }*/
                 });
 
                 this.connectSocketServer();
 
-                return res.data;
+                // TODO: maybe trigger promise only when connexion is established?
+                let promise = new Promise<ConnexionInterface>((resolve, reject) => {
+                    /*console.log('PROMISE CREATED')
+                    this.socket.on('connection', () => {
+                        console.log('CONNECTED');
+                        resolve(this);
+                    });*/
+                    resolve(this);
+                });
+
+                return promise;
+
+         /*       return res.data;
             })
             .catch((err) => {
                 console.error(err);
                 throw err;
-            });
+            });*/
     }
 
     /**
@@ -229,6 +242,7 @@ export class Connexion implements ConnexionInterface {
         }
 
         //listen event
+        this.attributeUserId();
         this.positionOfAllUser();
         this.disconnectServer();
         this.errorMessage();
@@ -286,6 +300,15 @@ export class Connexion implements ConnexionInterface {
         this.socket.emit(EventMessage.USER_POSITION, messageUserPosition.toString());
     }
 
+    attributeUserId(): void {
+        // This event is received as soon as the connexion is established.
+        // It allows informing the browser of its own user id.
+        this.socket.on(EventMessage.ATTRIBUTE_USER_ID, (userId: string) => {
+            console.log('Received my user id: ', userId);
+            this.userId = userId;
+        });
+    }
+
     /**
      * The data sent is an array with information for each user :
      * [
diff --git a/front/src/Phaser/Game/GameManager.ts b/front/src/Phaser/Game/GameManager.ts
index 6a4381dd..b886de9e 100644
--- a/front/src/Phaser/Game/GameManager.ts
+++ b/front/src/Phaser/Game/GameManager.ts
@@ -67,7 +67,7 @@ export class GameManager {
      */
     createCurrentPlayer(): void {
         //Get started room send by the backend
-        this.currentGameScene.createCurrentPlayer(this.ConnexionInstance.userId);
+        this.currentGameScene.createCurrentPlayer();
         this.status = StatusGameManagerEnum.CURRENT_USER_CREATED;
     }
 
@@ -119,6 +119,10 @@ export class GameManager {
         return this.playerName;
     }
 
+    getPlayerId(): string {
+        return this.ConnexionInstance.userId;
+    }
+
     getCharacterSelected(): string {
         return this.characterUserSelected;
     }
diff --git a/front/src/Phaser/Game/GameScene.ts b/front/src/Phaser/Game/GameScene.ts
index 7b32e3ef..1e4d1e6e 100644
--- a/front/src/Phaser/Game/GameScene.ts
+++ b/front/src/Phaser/Game/GameScene.ts
@@ -15,7 +15,7 @@ export enum Textures {
 
 export interface GameSceneInterface extends Phaser.Scene {
     Map: Phaser.Tilemaps.Tilemap;
-    createCurrentPlayer(UserId : string) : void;
+    createCurrentPlayer() : void;
     shareUserPosition(UsersPosition : Array<MessageUserPositionInterface>): void;
     shareGroupPosition(groupPositionMessage: GroupCreatedUpdatedMessageInterface): void;
     updateOrCreateMapPlayer(UsersPosition : Array<MessageUserPositionInterface>): void;
@@ -266,11 +266,11 @@ export class GameScene extends Phaser.Scene implements GameSceneInterface, Creat
         })
     }
 
-    createCurrentPlayer(UserId : string){
+    createCurrentPlayer(){
         //initialise player
         //TODO create animation moving between exit and strat
         this.CurrentPlayer = new Player(
-            UserId,
+            null, // The current player is not has no id (because the id can change if connexion is lost and we should check that id using the GameManager.
             this,
             this.startX,
             this.startY,
@@ -347,9 +347,11 @@ export class GameScene extends Phaser.Scene implements GameSceneInterface, Creat
             return;
         }
 
+        let currentPlayerId = this.GameManager.getPlayerId();
+
         //add or create new user
         UsersPosition.forEach((userPosition : MessageUserPositionInterface) => {
-            if(userPosition.userId === this.CurrentPlayer.userId){
+            if(userPosition.userId === currentPlayerId){
                 return;
             }
             let player = this.findPlayerInMap(userPosition.userId);
diff --git a/front/src/Phaser/Login/LogincScene.ts b/front/src/Phaser/Login/LogincScene.ts
index ea21e9f5..f7dd0029 100644
--- a/front/src/Phaser/Login/LogincScene.ts
+++ b/front/src/Phaser/Login/LogincScene.ts
@@ -90,7 +90,7 @@ export class LogincScene extends Phaser.Scene implements GameSceneInterface {
         });
 
         /*create user*/
-        this.createCurrentPlayer("test");
+        this.createCurrentPlayer();
         cypressAsserter.initFinished();
     }
 
@@ -144,7 +144,7 @@ export class LogincScene extends Phaser.Scene implements GameSceneInterface {
         throw new Error("Method not implemented.");
     }
 
-    createCurrentPlayer(UserId: string): void {
+    createCurrentPlayer(): void {
         for (let i = 0; i <PLAYER_RESOURCES.length; i++) {
             let playerResource = PLAYER_RESOURCES[i];
             let player = this.physics.add.sprite(playerResource.x, playerResource.y, playerResource.name, playerResource.name);
diff --git a/front/src/Phaser/Player/Player.ts b/front/src/Phaser/Player/Player.ts
index 932f889d..dd33bd3c 100644
--- a/front/src/Phaser/Player/Player.ts
+++ b/front/src/Phaser/Player/Player.ts
@@ -7,7 +7,6 @@ import {PlayableCaracter} from "../Entity/PlayableCaracter";
 
 export const hasMovedEventName = "hasMoved";
 export interface CurrentGamerInterface extends PlayableCaracter{
-    userId : string;
     initAnimation() : void;
     moveUser(delta: number) : void;
     say(text : string) : void;