diff --git a/src/client/app.tsx b/src/client/app.tsx
index 8352c09..ae385d3 100644
--- a/src/client/app.tsx
+++ b/src/client/app.tsx
@@ -1,16 +1,39 @@
 import { useState } from "react";
+import { useAuth } from "@/client/components/auth-provider";
+import { LoginForm } from "@/client/components/login-form";
+import { UserProfile } from "@/client/components/user-profile";
 import { BookingForm } from "@/client/components/booking-form";
 import { AdminTreatments } from "@/client/components/admin-treatments";
 import { AdminBookings } from "@/client/components/admin-bookings";
 import { InitialDataLoader } from "@/client/components/initial-data-loader";
 
 function App() {
-  const [activeTab, setActiveTab] = useState<"booking" | "admin-treatments" | "admin-bookings">("booking");
+  const { user, isLoading, isOwner } = useAuth();
+  const [activeTab, setActiveTab] = useState<"booking" | "admin-treatments" | "admin-bookings" | "profile">("booking");
+
+  // Show loading spinner while checking authentication
+  if (isLoading) {
+    return (
+      <div className="min-h-screen flex items-center justify-center bg-gradient-to-br from-pink-50 to-purple-50">
+        <div className="text-center">
+          <div className="text-6xl mb-4">💅</div>
+          <div className="text-lg text-gray-600">Lade...</div>
+        </div>
+      </div>
+    );
+  }
+
+  // Show login form if user is not authenticated and trying to access admin features
+  const needsAuth = !user && (activeTab === "admin-treatments" || activeTab === "admin-bookings" || activeTab === "profile");
+  if (needsAuth) {
+    return <LoginForm />;
+  }
 
   const tabs = [
-    { id: "booking", label: "Book Appointment", icon: "📅" },
-    { id: "admin-treatments", label: "Manage Treatments", icon: "💅" },
-    { id: "admin-bookings", label: "Manage Bookings", icon: "📋" },
+    { id: "booking", label: "Termin buchen", icon: "📅", requiresAuth: false },
+    { id: "admin-treatments", label: "Behandlungen verwalten", icon: "💅", requiresAuth: true },
+    { id: "admin-bookings", label: "Buchungen verwalten", icon: "📋", requiresAuth: true },
+    ...(user ? [{ id: "profile", label: "Profil", icon: "👤", requiresAuth: true }] : []),
   ] as const;
 
   return (
@@ -28,6 +51,19 @@ function App() {
                 <p className="text-sm text-gray-600">Professional Nail Design & Care</p>
               </div>
             </div>
+            
+            {user && (
+              <div className="flex items-center space-x-4">
+                <span className="text-sm text-gray-600">
+                  Willkommen, {user.username}
+                </span>
+                {isOwner && (
+                  <span className="bg-pink-100 text-pink-800 px-2 py-1 rounded-full text-xs font-medium">
+                    Inhaber
+                  </span>
+                )}
+              </div>
+            )}
           </div>
         </div>
       </header>
@@ -36,20 +72,44 @@ function App() {
       <nav className="bg-white shadow-sm">
         <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
           <div className="flex space-x-8">
-            {tabs.map((tab) => (
+            {tabs.map((tab) => {
+              // Hide admin tabs for non-owners
+              if (tab.requiresAuth && !isOwner && tab.id !== "profile") {
+                return null;
+              }
+              
+              return (
+                <button
+                  key={tab.id}
+                  onClick={() => {
+                    if (tab.requiresAuth && !user) {
+                      // This will trigger the login form
+                      setActiveTab(tab.id as any);
+                    } else {
+                      setActiveTab(tab.id as any);
+                    }
+                  }}
+                  className={`py-4 px-1 border-b-2 font-medium text-sm flex items-center space-x-2 ${
+                    activeTab === tab.id
+                      ? "border-pink-500 text-pink-600"
+                      : "border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300"
+                  }`}
+                >
+                  <span>{tab.icon}</span>
+                  <span>{tab.label}</span>
+                </button>
+              );
+            })}
+            
+            {!user && (
               <button
-                key={tab.id}
-                onClick={() => setActiveTab(tab.id)}
-                className={`py-4 px-1 border-b-2 font-medium text-sm flex items-center space-x-2 ${
-                  activeTab === tab.id
-                    ? "border-pink-500 text-pink-600"
-                    : "border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300"
-                }`}
+                onClick={() => setActiveTab("profile")} // This will trigger login
+                className="py-4 px-1 border-b-2 border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300 font-medium text-sm flex items-center space-x-2"
               >
-                <span>{tab.icon}</span>
-                <span>{tab.label}</span>
+                <span>🔑</span>
+                <span>Inhaber Login</span>
               </button>
-            ))}
+            )}
           </div>
         </div>
       </nav>
@@ -60,44 +120,58 @@ function App() {
           <div>
             <div className="text-center mb-8">
               <h2 className="text-3xl font-bold text-gray-900 mb-4">
-                Book Your Perfect Nail Treatment
+                Buchen Sie Ihre perfekte Nagelbehandlung
               </h2>
               <p className="text-lg text-gray-600 max-w-2xl mx-auto">
-                Experience professional nail care with our expert technicians. 
-                Choose from our wide range of treatments and book your appointment today.
+                Erleben Sie professionelle Nagelpflege mit unseren Experten. 
+                Wählen Sie aus unserem breiten Angebot an Behandlungen und buchen Sie noch heute Ihren Termin.
               </p>
             </div>
             <BookingForm />
           </div>
         )}
 
-        {activeTab === "admin-treatments" && (
+        {activeTab === "admin-treatments" && isOwner && (
           <div>
             <div className="text-center mb-8">
               <h2 className="text-3xl font-bold text-gray-900 mb-4">
-                Treatment Management
+                Behandlungen verwalten
               </h2>
               <p className="text-lg text-gray-600">
-                Add, edit, and manage your nail treatment services.
+                Hinzufügen, bearbeiten und verwalten Sie Ihre Nagelbehandlungen.
               </p>
             </div>
             <AdminTreatments />
           </div>
         )}
 
-        {activeTab === "admin-bookings" && (
+        {activeTab === "admin-bookings" && isOwner && (
           <div>
             <div className="text-center mb-8">
               <h2 className="text-3xl font-bold text-gray-900 mb-4">
-                Booking Management
+                Buchungen verwalten
               </h2>
               <p className="text-lg text-gray-600">
-                View and manage customer appointments and bookings.
+                Sehen und verwalten Sie Kundentermine und Buchungen.
               </p>
             </div>
             <AdminBookings />
           </div>
         )}
+
+        {activeTab === "profile" && user && (
+          <div>
+            <div className="text-center mb-8">
+              <h2 className="text-3xl font-bold text-gray-900 mb-4">
+                Benutzerprofil
+              </h2>
+              <p className="text-lg text-gray-600">
+                Verwalten Sie Ihre Kontoinformationen und Einstellungen.
+              </p>
+            </div>
+            <UserProfile />
+          </div>
+        )}
       </main>
 
       {/* Footer */}
diff --git a/src/client/components/auth-provider.tsx b/src/client/components/auth-provider.tsx
new file mode 100644
index 0000000..bdd38a7
--- /dev/null
+++ b/src/client/components/auth-provider.tsx
@@ -0,0 +1,114 @@
+import { createContext, useContext, useState, useEffect, ReactNode } from "react";
+import { useMutation } from "@tanstack/react-query";
+import { queryClient } from "@/client/rpc-client";
+
+interface User {
+  id: string;
+  username: string;
+  email: string;
+  role: "customer" | "owner";
+}
+
+interface AuthContextType {
+  user: User | null;
+  sessionId: string | null;
+  isLoading: boolean;
+  login: (username: string, password: string) => Promise<void>;
+  logout: () => void;
+  isOwner: boolean;
+}
+
+const AuthContext = createContext<AuthContextType | null>(null);
+
+export function useAuth() {
+  const context = useContext(AuthContext);
+  if (!context) {
+    throw new Error("useAuth must be used within an AuthProvider");
+  }
+  return context;
+}
+
+interface AuthProviderProps {
+  children: ReactNode;
+}
+
+export function AuthProvider({ children }: AuthProviderProps) {
+  const [user, setUser] = useState<User | null>(null);
+  const [sessionId, setSessionId] = useState<string | null>(null);
+  const [isLoading, setIsLoading] = useState(true);
+
+  const { mutateAsync: loginMutation } = useMutation(
+    queryClient.auth.login.mutationOptions()
+  );
+
+  const { mutateAsync: logoutMutation } = useMutation(
+    queryClient.auth.logout.mutationOptions()
+  );
+
+  const { mutateAsync: verifySessionMutation } = useMutation(
+    queryClient.auth.verifySession.mutationOptions()
+  );
+
+  useEffect(() => {
+    // Check for existing session on app load
+    const storedSessionId = localStorage.getItem("sessionId");
+    if (storedSessionId) {
+      verifySessionMutation(storedSessionId)
+        .then((result) => {
+          setUser(result.user);
+          setSessionId(storedSessionId);
+        })
+        .catch(() => {
+          localStorage.removeItem("sessionId");
+        })
+        .finally(() => {
+          setIsLoading(false);
+        });
+    } else {
+      setIsLoading(false);
+    }
+  }, [verifySessionMutation]);
+
+  const login = async (username: string, password: string) => {
+    try {
+      const result = await loginMutation({ username, password });
+      setUser(result.user);
+      setSessionId(result.sessionId);
+      localStorage.setItem("sessionId", result.sessionId);
+    } catch (error) {
+      throw error;
+    }
+  };
+
+  const logout = async () => {
+    if (sessionId) {
+      try {
+        await logoutMutation(sessionId);
+      } catch (error) {
+        // Continue with logout even if server call fails
+        console.error("Logout error:", error);
+      }
+    }
+    
+    setUser(null);
+    setSessionId(null);
+    localStorage.removeItem("sessionId");
+  };
+
+  const isOwner = user?.role === "owner";
+
+  const value: AuthContextType = {
+    user,
+    sessionId,
+    isLoading,
+    login,
+    logout,
+    isOwner,
+  };
+
+  return (
+    <AuthContext.Provider value={value}>
+      {children}
+    </AuthContext.Provider>
+  );
+}
\ No newline at end of file
diff --git a/src/client/components/booking-form.tsx b/src/client/components/booking-form.tsx
index 5983c6b..e29ebc0 100644
--- a/src/client/components/booking-form.tsx
+++ b/src/client/components/booking-form.tsx
@@ -64,7 +64,7 @@ export function BookingForm() {
   const handleSubmit = (e: React.FormEvent) => {
     e.preventDefault();
     if (!selectedTreatment || !customerName || !customerEmail || !customerPhone || !appointmentDate || !appointmentTime) {
-      alert("Please fill in all required fields");
+      alert("Bitte füllen Sie alle erforderlichen Felder aus");
       return;
     }
 
@@ -85,7 +85,7 @@ export function BookingForm() {
         setAppointmentDate("");
         setAppointmentTime("");
         setNotes("");
-        alert("Booking created successfully! We'll contact you to confirm your appointment.");
+        alert("Buchung erfolgreich erstellt! Wir werden Sie kontaktieren, um Ihren Termin zu bestätigen.");
       }
     });
   };
@@ -95,13 +95,13 @@ export function BookingForm() {
 
   return (
     <div className="max-w-2xl mx-auto bg-white rounded-lg shadow-lg p-6">
-      <h2 className="text-2xl font-bold text-gray-900 mb-6">Book Your Nail Treatment</h2>
+      <h2 className="text-2xl font-bold text-gray-900 mb-6">Buchen Sie Ihre Nagelbehandlung</h2>
       
       <form onSubmit={handleSubmit} className="space-y-6">
         {/* Treatment Selection */}
         <div>
           <label className="block text-sm font-medium text-gray-700 mb-2">
-            Select Treatment *
+            Behandlung auswählen *
           </label>
           <select
             value={selectedTreatment}
@@ -109,7 +109,7 @@ export function BookingForm() {
             className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
             required
           >
-            <option value="">Choose a treatment</option>
+            <option value="">Wählen Sie eine Behandlung</option>
             {treatments?.map((treatment) => (
               <option key={treatment.id} value={treatment.id}>
                 {treatment.name} - ${(treatment.price / 100).toFixed(2)} ({treatment.duration} min)
@@ -125,7 +125,7 @@ export function BookingForm() {
         <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
           <div>
             <label className="block text-sm font-medium text-gray-700 mb-2">
-              Full Name *
+              Vollständiger Name *
             </label>
             <input
               type="text"
@@ -137,7 +137,7 @@ export function BookingForm() {
           </div>
           <div>
             <label className="block text-sm font-medium text-gray-700 mb-2">
-              Email *
+              E-Mail *
             </label>
             <input
               type="email"
@@ -151,7 +151,7 @@ export function BookingForm() {
 
         <div>
           <label className="block text-sm font-medium text-gray-700 mb-2">
-            Phone Number *
+            Telefonnummer *
           </label>
           <input
             type="tel"
@@ -166,7 +166,7 @@ export function BookingForm() {
         <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
           <div>
             <label className="block text-sm font-medium text-gray-700 mb-2">
-              Preferred Date *
+              Gewünschtes Datum *
             </label>
             <input
               type="date"
@@ -179,7 +179,7 @@ export function BookingForm() {
           </div>
           <div>
             <label className="block text-sm font-medium text-gray-700 mb-2">
-              Preferred Time *
+              Gewünschte Uhrzeit *
             </label>
             <select
               value={appointmentTime}
@@ -188,7 +188,7 @@ export function BookingForm() {
               disabled={!appointmentDate || !selectedTreatment}
               required
             >
-              <option value="">Select time</option>
+              <option value="">Zeit auswählen</option>
               {availableTimeSlots.map((time) => (
                 <option key={time} value={time}>
                   {time}
@@ -201,14 +201,14 @@ export function BookingForm() {
         {/* Notes */}
         <div>
           <label className="block text-sm font-medium text-gray-700 mb-2">
-            Additional Notes
+            Zusätzliche Notizen
           </label>
           <textarea
             value={notes}
             onChange={(e) => setNotes(e.target.value)}
             rows={3}
             className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
-            placeholder="Any special requests or information..."
+            placeholder="Besondere Wünsche oder Informationen..."
           />
         </div>
 
@@ -217,7 +217,7 @@ export function BookingForm() {
           disabled={isPending}
           className="w-full bg-pink-600 text-white py-3 px-4 rounded-md hover:bg-pink-700 focus:ring-2 focus:ring-pink-500 focus:ring-offset-2 disabled:opacity-50 disabled:cursor-not-allowed font-medium"
         >
-          {isPending ? "Booking..." : "Book Appointment"}
+          {isPending ? "Wird gebucht..." : "Termin buchen"}
         </button>
       </form>
     </div>
diff --git a/src/client/components/login-form.tsx b/src/client/components/login-form.tsx
new file mode 100644
index 0000000..477e743
--- /dev/null
+++ b/src/client/components/login-form.tsx
@@ -0,0 +1,85 @@
+import { useState } from "react";
+import { useAuth } from "@/client/components/auth-provider";
+
+export function LoginForm() {
+  const [username, setUsername] = useState("");
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState("");
+  const [isLoading, setIsLoading] = useState(false);
+  
+  const { login } = useAuth();
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault();
+    setError("");
+    setIsLoading(true);
+
+    try {
+      await login(username, password);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Login failed");
+    } finally {
+      setIsLoading(false);
+    }
+  };
+
+  return (
+    <div className="min-h-screen flex items-center justify-center bg-gradient-to-br from-pink-50 to-purple-50">
+      <div className="max-w-md w-full space-y-8 p-8">
+        <div className="text-center">
+          <div className="text-6xl mb-4">💅</div>
+          <h2 className="text-3xl font-bold text-gray-900">Stargirlnails Kiel</h2>
+          <p className="mt-2 text-sm text-gray-600">Inhaber Login</p>
+        </div>
+        
+        <form className="mt-8 space-y-6 bg-white p-6 rounded-lg shadow-lg" onSubmit={handleSubmit}>
+          {error && (
+            <div className="bg-red-50 border border-red-200 text-red-700 px-4 py-3 rounded">
+              {error}
+            </div>
+          )}
+          
+          <div>
+            <label className="block text-sm font-medium text-gray-700 mb-2">
+              Benutzername
+            </label>
+            <input
+              type="text"
+              value={username}
+              onChange={(e) => setUsername(e.target.value)}
+              className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
+              required
+            />
+          </div>
+          
+          <div>
+            <label className="block text-sm font-medium text-gray-700 mb-2">
+              Passwort
+            </label>
+            <input
+              type="password"
+              value={password}
+              onChange={(e) => setPassword(e.target.value)}
+              className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
+              required
+            />
+          </div>
+          
+          <button
+            type="submit"
+            disabled={isLoading}
+            className="w-full bg-pink-600 text-white py-3 px-4 rounded-md hover:bg-pink-700 focus:ring-2 focus:ring-pink-500 focus:ring-offset-2 disabled:opacity-50 disabled:cursor-not-allowed font-medium"
+          >
+            {isLoading ? "Anmelden..." : "Anmelden"}
+          </button>
+        </form>
+        
+        <div className="text-center text-sm text-gray-600">
+          <p>Standard Login:</p>
+          <p className="font-mono">Benutzername: owner</p>
+          <p className="font-mono">Passwort: admin123</p>
+        </div>
+      </div>
+    </div>
+  );
+}
\ No newline at end of file
diff --git a/src/client/components/user-profile.tsx b/src/client/components/user-profile.tsx
new file mode 100644
index 0000000..5337d4f
--- /dev/null
+++ b/src/client/components/user-profile.tsx
@@ -0,0 +1,165 @@
+import { useState } from "react";
+import { useMutation } from "@tanstack/react-query";
+import { useAuth } from "@/client/components/auth-provider";
+import { queryClient } from "@/client/rpc-client";
+
+export function UserProfile() {
+  const { user, sessionId, logout } = useAuth();
+  const [showPasswordChange, setShowPasswordChange] = useState(false);
+  const [currentPassword, setCurrentPassword] = useState("");
+  const [newPassword, setNewPassword] = useState("");
+  const [confirmPassword, setConfirmPassword] = useState("");
+  const [message, setMessage] = useState("");
+  const [error, setError] = useState("");
+
+  const { mutate: changePassword, isPending } = useMutation(
+    queryClient.auth.changePassword.mutationOptions()
+  );
+
+  const handlePasswordChange = (e: React.FormEvent) => {
+    e.preventDefault();
+    setError("");
+    setMessage("");
+
+    if (newPassword !== confirmPassword) {
+      setError("Neue Passwörter stimmen nicht überein");
+      return;
+    }
+
+    if (newPassword.length < 6) {
+      setError("Neues Passwort muss mindestens 6 Zeichen lang sein");
+      return;
+    }
+
+    if (!sessionId) {
+      setError("Keine gültige Sitzung");
+      return;
+    }
+
+    changePassword({
+      sessionId,
+      currentPassword,
+      newPassword,
+    }, {
+      onSuccess: () => {
+        setMessage("Passwort erfolgreich geändert");
+        setCurrentPassword("");
+        setNewPassword("");
+        setConfirmPassword("");
+        setShowPasswordChange(false);
+      },
+      onError: (err) => {
+        setError(err instanceof Error ? err.message : "Fehler beim Ändern des Passworts");
+      }
+    });
+  };
+
+  if (!user) return null;
+
+  return (
+    <div className="bg-white rounded-lg shadow-lg p-6 max-w-2xl mx-auto">
+      <div className="flex justify-between items-center mb-6">
+        <h2 className="text-2xl font-bold text-gray-900">Benutzerprofil</h2>
+        <button
+          onClick={logout}
+          className="bg-red-600 text-white px-4 py-2 rounded-md hover:bg-red-700 font-medium"
+        >
+          Abmelden
+        </button>
+      </div>
+
+      <div className="space-y-4 mb-6">
+        <div>
+          <label className="block text-sm font-medium text-gray-700">Benutzername</label>
+          <p className="mt-1 text-lg text-gray-900">{user.username}</p>
+        </div>
+        
+        <div>
+          <label className="block text-sm font-medium text-gray-700">E-Mail</label>
+          <p className="mt-1 text-lg text-gray-900">{user.email}</p>
+        </div>
+        
+        <div>
+          <label className="block text-sm font-medium text-gray-700">Rolle</label>
+          <p className="mt-1 text-lg text-gray-900 capitalize">{user.role === "owner" ? "Inhaber" : "Kunde"}</p>
+        </div>
+      </div>
+
+      <div>
+        <button
+          onClick={() => setShowPasswordChange(!showPasswordChange)}
+          className="bg-pink-600 text-white px-4 py-2 rounded-md hover:bg-pink-700 font-medium"
+        >
+          {showPasswordChange ? "Abbrechen" : "Passwort ändern"}
+        </button>
+      </div>
+
+      {showPasswordChange && (
+        <form onSubmit={handlePasswordChange} className="mt-6 space-y-4 border-t pt-6">
+          <h3 className="text-lg font-semibold text-gray-900">Passwort ändern</h3>
+          
+          {error && (
+            <div className="bg-red-50 border border-red-200 text-red-700 px-4 py-3 rounded">
+              {error}
+            </div>
+          )}
+          
+          {message && (
+            <div className="bg-green-50 border border-green-200 text-green-700 px-4 py-3 rounded">
+              {message}
+            </div>
+          )}
+
+          <div>
+            <label className="block text-sm font-medium text-gray-700 mb-2">
+              Aktuelles Passwort
+            </label>
+            <input
+              type="password"
+              value={currentPassword}
+              onChange={(e) => setCurrentPassword(e.target.value)}
+              className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
+              required
+            />
+          </div>
+
+          <div>
+            <label className="block text-sm font-medium text-gray-700 mb-2">
+              Neues Passwort
+            </label>
+            <input
+              type="password"
+              value={newPassword}
+              onChange={(e) => setNewPassword(e.target.value)}
+              className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
+              minLength={6}
+              required
+            />
+          </div>
+
+          <div>
+            <label className="block text-sm font-medium text-gray-700 mb-2">
+              Neues Passwort bestätigen
+            </label>
+            <input
+              type="password"
+              value={confirmPassword}
+              onChange={(e) => setConfirmPassword(e.target.value)}
+              className="w-full p-3 border border-gray-300 rounded-md focus:ring-2 focus:ring-pink-500 focus:border-pink-500"
+              minLength={6}
+              required
+            />
+          </div>
+
+          <button
+            type="submit"
+            disabled={isPending}
+            className="bg-pink-600 text-white px-4 py-2 rounded-md hover:bg-pink-700 disabled:opacity-50 font-medium"
+          >
+            {isPending ? "Ändern..." : "Passwort ändern"}
+          </button>
+        </form>
+      )}
+    </div>
+  );
+}
\ No newline at end of file
diff --git a/src/client/main.tsx b/src/client/main.tsx
index 172dba0..73e8e66 100644
--- a/src/client/main.tsx
+++ b/src/client/main.tsx
@@ -1,15 +1,18 @@
-import { StrictMode } from "react";
-import { createRoot } from "react-dom/client";
-import "./styles/globals.css";
-import App from "./app.tsx";
-import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
-
-const queryClient = new QueryClient();
-
-createRoot(document.getElementById("root")!).render(
-  <StrictMode>
-    <QueryClientProvider client={queryClient}>
-      <App />
-    </QueryClientProvider>
-  </StrictMode>,
-);
+import { StrictMode } from "react";
+import { createRoot } from "react-dom/client";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { AuthProvider } from "@/client/components/auth-provider";
+import App from "./app.tsx";
+import "./styles/globals.css";
+
+const queryClient = new QueryClient();
+
+createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <QueryClientProvider client={queryClient}>
+      <AuthProvider>
+        <App />
+      </AuthProvider>
+    </QueryClientProvider>
+  </StrictMode>
+);
diff --git a/src/server/rpc/auth.ts b/src/server/rpc/auth.ts
new file mode 100644
index 0000000..a78a3fa
--- /dev/null
+++ b/src/server/rpc/auth.ts
@@ -0,0 +1,165 @@
+import { call, os } from "@orpc/server";
+import { z } from "zod";
+import { randomUUID } from "crypto";
+import { createKV } from "@/server/lib/create-kv";
+
+const UserSchema = z.object({
+  id: z.string(),
+  username: z.string(),
+  email: z.string(),
+  passwordHash: z.string(),
+  role: z.enum(["customer", "owner"]),
+  createdAt: z.string(),
+});
+
+const SessionSchema = z.object({
+  id: z.string(),
+  userId: z.string(),
+  expiresAt: z.string(),
+  createdAt: z.string(),
+});
+
+type User = z.output<typeof UserSchema>;
+type Session = z.output<typeof SessionSchema>;
+
+const usersKV = createKV<User>("users");
+const sessionsKV = createKV<Session>("sessions");
+
+// Simple password hashing (in production, use bcrypt or similar)
+const hashPassword = (password: string): string => {
+  return Buffer.from(password).toString('base64');
+};
+
+const verifyPassword = (password: string, hash: string): boolean => {
+  return hashPassword(password) === hash;
+};
+
+// Initialize default owner account
+const initializeOwner = async () => {
+  const existingUsers = await usersKV.getAllItems();
+  if (existingUsers.length === 0) {
+    const ownerId = randomUUID();
+    const owner: User = {
+      id: ownerId,
+      username: "owner",
+      email: "owner@stargirlnails.de",
+      passwordHash: hashPassword("admin123"), // Default password
+      role: "owner",
+      createdAt: new Date().toISOString(),
+    };
+    await usersKV.setItem(ownerId, owner);
+  }
+};
+
+// Initialize on module load
+initializeOwner();
+
+const login = os
+  .input(z.object({
+    username: z.string(),
+    password: z.string(),
+  }))
+  .handler(async ({ input }) => {
+    const users = await usersKV.getAllItems();
+    const user = users.find(u => u.username === input.username);
+    
+    if (!user || !verifyPassword(input.password, user.passwordHash)) {
+      throw new Error("Invalid credentials");
+    }
+
+    // Create session
+    const sessionId = randomUUID();
+    const expiresAt = new Date();
+    expiresAt.setHours(expiresAt.getHours() + 24); // 24 hours
+
+    const session: Session = {
+      id: sessionId,
+      userId: user.id,
+      expiresAt: expiresAt.toISOString(),
+      createdAt: new Date().toISOString(),
+    };
+
+    await sessionsKV.setItem(sessionId, session);
+
+    return {
+      sessionId,
+      user: {
+        id: user.id,
+        username: user.username,
+        email: user.email,
+        role: user.role,
+      },
+    };
+  });
+
+const logout = os
+  .input(z.string()) // sessionId
+  .handler(async ({ input }) => {
+    await sessionsKV.removeItem(input);
+    return { success: true };
+  });
+
+const verifySession = os
+  .input(z.string()) // sessionId
+  .handler(async ({ input }) => {
+    const session = await sessionsKV.getItem(input);
+    if (!session) {
+      throw new Error("Invalid session");
+    }
+
+    if (new Date(session.expiresAt) < new Date()) {
+      await sessionsKV.removeItem(input);
+      throw new Error("Session expired");
+    }
+
+    const user = await usersKV.getItem(session.userId);
+    if (!user) {
+      throw new Error("User not found");
+    }
+
+    return {
+      user: {
+        id: user.id,
+        username: user.username,
+        email: user.email,
+        role: user.role,
+      },
+    };
+  });
+
+const changePassword = os
+  .input(z.object({
+    sessionId: z.string(),
+    currentPassword: z.string(),
+    newPassword: z.string(),
+  }))
+  .handler(async ({ input }) => {
+    const session = await sessionsKV.getItem(input.sessionId);
+    if (!session) {
+      throw new Error("Invalid session");
+    }
+
+    const user = await usersKV.getItem(session.userId);
+    if (!user) {
+      throw new Error("User not found");
+    }
+
+    if (!verifyPassword(input.currentPassword, user.passwordHash)) {
+      throw new Error("Current password is incorrect");
+    }
+
+    const updatedUser = {
+      ...user,
+      passwordHash: hashPassword(input.newPassword),
+    };
+
+    await usersKV.setItem(user.id, updatedUser);
+    return { success: true };
+  });
+
+export const router = {
+  login,
+  logout,
+  verifySession,
+  changePassword,
+};
\ No newline at end of file
diff --git a/src/server/rpc/index.ts b/src/server/rpc/index.ts
index 39712a5..8f55d27 100644
--- a/src/server/rpc/index.ts
+++ b/src/server/rpc/index.ts
@@ -1,9 +1,11 @@
 import { demo } from "./demo";
 import { router as treatments } from "./treatments";
 import { router as bookings } from "./bookings";
+import { router as auth } from "./auth";
 
 export const router = {
   demo,
   treatments,
   bookings,
+  auth,
 };