fix: fix some stuff

frontend/src/app/service/user.service.ts

@@ -1,7 +1,8 @@
 import { inject, Injectable } from '@angular/core';
 import { HttpClient } from '@angular/common/http';
 import { KeycloakProfile } from 'keycloak-js';
-import { async } from 'rxjs';
+import { async, Observable } from 'rxjs';
+import { User } from '../model/User';
 
 @Injectable({
   providedIn: 'root',
@@ -9,18 +10,18 @@ import { async } from 'rxjs';
 export class UserService {
   private http: HttpClient = inject(HttpClient);
 
-  public getUser(id: string) {
-    return this.http.get<{ keycloakId: string, username: string } | null>(`/backend/user/${id}`);
+  public getUser(id: string): Observable<User|null> {
+    return this.http.get<User|null>(`/backend/user/${id}`);
   }
 
-  public createUser(id: string, username: string) {
-    return this.http.post<{ keycloakId: string, username: string }>('/backend/user', {
+  public createUser(id: string, username: string): Observable<User> {
+    return this.http.post<User>('/backend/user', {
       keycloakId: id,
       username: username,
     });
   }
 
-  public async getCurrentUser(userProfile: KeycloakProfile) {
+  public async getOrCreateUser(userProfile: KeycloakProfile) {
     if (userProfile.id == null) {
       return;
     }