Send data from WIFI Shield to a protected webserver

Hi,
I try to send data from my WIFI Shield to my Internet webserver.
When the Webpage is not protected then is good.
Now the page is protected and it comes a login windows

how and what must I do on my sketch that will funktion.

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#include <SPI.h>
#include <WiFi.h>
#include <WiFiClient.h>
#include <WiFiServer.h>
#include <WiFiUdp.h>

char ssid[] = "FRITZ!Box 3272";
char password[] = "xxxxxxxxxxxxxxxxxxxxxxxx";
int status = WL_IDLE_STATUS;
WiFiClient client;

char server[] = "www.xxxxxxx.xx.xx";
String data;
String A;
String B;

void setup() {
Serial.begin(9600);
connectWifi();
printWifiStatus();
}

void loop() {

String data;
A = "data=1111&";
B = "data2=2222";
data= A+B;

if (client.connect(server,80)) {
Serial.println("connected");
client.println("POST /weberei/WEBMC_Arduino.php HTTP/1.1");
client.println("Host: www.xxxxxxx.xx.xx");
client.println("Content-Type: application/x-www-form-urlencoded");
client.print("Content-Length: ");
client.println(data.length());
client.println("Connection: close");
client.println();
client.print(data);
client.println();

Serial.println("POST /weberei/WEBMC_Arduino.php HTTP/1.1");
Serial.println("Host: www.xxxxxxx.xx.xx");
Serial.println("Content-Type: application/x-www-form-urlencoded");
Serial.print("Content-Length: ");
Serial.println(data.length());
Serial.println("Connection: close");
Serial.println();
Serial.print(data);
Serial.println();
}
delay(10000);

if (client.connected()) {
Serial.println();
Serial.println("disconnecting.");
client.stop();
}
}

void connectWifi() {
// Attempt to connect to wifi network
while ( status != WL_CONNECTED) {
Serial.print("Attempting to connect to SSID: ");
Serial.println(ssid);
status = WiFi.begin(ssid, password);
// Wait 10 seconds for connection
delay(10000);
}
}

void printWifiStatus() {
// Print the SSID of the network you're attached to
Serial.print("SSID: ");
Serial.println(WiFi.SSID());

// Print your WiFi shield's IP address
IPAddress ip = WiFi.localIP();
Serial.print("IP Address: ");
Serial.println(ip);

// Print the received signal strength
long rssi = WiFi.RSSI();
Serial.print("signal strength (RSSI):");
Serial.print(rssi);
Serial.println(" dBm");
}

Now the page is protected and it comes a login windows

What page? The Arduino is a client, making a POST request (though it isn't clear why you are not using the easier GET request).

Use wireshark or similar to see what HTTP request gets sent when you log in to the web site with an ordinary browser, and then write your sketch to make a similar request.