refactor(frontend): Algemene linting fouten

frontend/src/services/auth/auth-service.ts

@@ -49,7 +49,7 @@ const isLoggedIn = computed(() => authState.user !== null);
 /**
  * Redirect the user to the login page where he/she can choose whether to log in as a student or teacher.
  */
-async function initiateLogin() {
+async function initiateLogin(): Promise<void> {
     await router.push(loginRoute);
 }
 
@@ -77,12 +77,12 @@ async function handleLoginCallback(): Promise<void> {
 /**
  * Refresh an expired authorization token.
  */
-async function renewToken() {
+async function renewToken(): Promise<User | null> {
     const activeRole = authStorage.getActiveRole();
     if (!activeRole) {
         console.log("Can't renew the token: Not logged in!");
         await initiateLogin();
-        return;
+        return null;
     }
     try {
         return await (await getUserManagers())[activeRole].signinSilent();
@@ -91,6 +91,7 @@ async function renewToken() {
         console.log(error);
         await initiateLogin();
     }
+    return null;
 }
 
 /**
@@ -113,7 +114,7 @@ apiClient.interceptors.request.use(
         }
         return reqConfig;
     },
-    (error) => Promise.reject(error),
+    async (error) => Promise.reject(error),
 );
 
 // Registering interceptor to refresh the token when a request failed because it was expired.
@@ -121,7 +122,7 @@ apiClient.interceptors.response.use(
     (response) => response,
     async (error: AxiosError<{ message?: string }>) => {
         if (error.response?.status === 401) {
-            if (error.response!.data.message === "token_expired") {
+            if (error.response.data.message === "token_expired") {
                 console.log("Access token expired, trying to refresh...");
                 await renewToken();
                 return apiClient(error.config!); // Retry the request