Implement authentication phase with Cidaas OAuth2 integration

- Add authentication middleware to protect routes
- Create API endpoints for login, logout, registration, and user info
- Develop UI components for login and registration forms
- Integrate VeeValidate for form validation
- Update environment configuration for Cidaas settings
- Add i18n support for English and German languages
- Enhance Tailwind CSS for improved styling of auth components
- Document authentication flow and testing procedures

app/composables/useAuth.ts

@@ -0,0 +1,91 @@
+// composables/useAuth.ts
+
+/**
+ * Authentication composable
+ *
+ * Wrapper around nuxt-auth-utils useUserSession() with convenience methods
+ *
+ * Usage:
+ * const { user, loggedIn, login, logout } = useAuth()
+ */
+
+export function useAuth() {
+  const { loggedIn, user, clear, fetch } = useUserSession()
+
+  /**
+   * Login with email
+   * Initiates OAuth2 flow
+   */
+  async function login(email: string) {
+    try {
+      // Call login endpoint to get redirect URL
+      const { redirectUrl } = await $fetch('/api/auth/login', {
+        method: 'POST',
+        body: { email },
+      })
+
+      // Redirect to Cidaas
+      navigateTo(redirectUrl, { external: true })
+    } catch (error) {
+      console.error('Login failed:', error)
+      throw error
+    }
+  }
+
+  /**
+   * Register new user
+   */
+  async function register(data: {
+    email: string
+    password: string
+    firstName: string
+    lastName: string
+  }) {
+    try {
+      const result = await $fetch('/api/auth/register', {
+        method: 'POST',
+        body: data,
+      })
+
+      return result
+    } catch (error) {
+      console.error('Registration failed:', error)
+      throw error
+    }
+  }
+
+  /**
+   * Logout
+   * Clears session and redirects to homepage
+   */
+  async function logout() {
+    try {
+      await $fetch('/api/auth/logout', { method: 'POST' })
+      await clear() // Clear client-side state
+      navigateTo('/') // Redirect to homepage
+    } catch (error) {
+      console.error('Logout failed:', error)
+      throw error
+    }
+  }
+
+  /**
+   * Refresh user data from server
+   */
+  async function refreshUser() {
+    try {
+      await fetch() // Re-fetch session from server
+    } catch (error) {
+      console.error('Refresh user failed:', error)
+    }
+  }
+
+  return {
+    user,
+    loggedIn,
+    login,
+    register,
+    logout,
+    refreshUser,
+  }
+}