UNO + ETHERNET + RC522

Hallo
I ask you for help because I start, I'm looking and I can not find it. I've got to do a project in which RC522 touch the card and on the website displays the card number. Combines and nothing works. Please improve the code, I did something like this:

/*
Web Server

A simple web server that shows the value of the analog input pins.
using an Arduino Wiznet Ethernet shield.

Circuit:

  • Ethernet shield attached to pins 10, 11, 12, 13
  • Analog inputs attached to pins A0 through A5 (optional)

created 18 Dec 2009
by David A. Mellis
modified 9 Apr 2012
by Tom Igoe
modified 02 Sept 2015
by Arturo Guadalupi

*/

#include <SPI.h>
#include <MFRC522.h>
#include <Ethernet.h>

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};
IPAddress ip(192, 168, 0, 177);

// Initialize the Ethernet server library
// with the IP address and port you want to use
// (port 80 is default for HTTP):
EthernetServer server(80);
#define SS_PIN 7
#define RST_PIN 6
MFRC522 mfrc522(SS_PIN, RST_PIN); // Create MFRC522 instance.
byte readCard[4];
String rfidUid = "";
String kartaauth1="9bd37725"; // deklaracja autoryzowanej karty

void setup() {

// Open serial communications and wait for port to open:
Serial.begin(9600);
SPI.begin(); // Init SPI bus
mfrc522.PCD_Init(); // Init MFRC522 card
Serial.println("Scan PICC to see UID and type...");
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only

}

// start the Ethernet connection and the server:
Ethernet.begin(mac, ip);
server.begin();
Serial.print("server is at ");
Serial.println(Ethernet.localIP());
}

void loop() {

{
// Look for new cards
if ( ! mfrc522.PICC_IsNewCardPresent()) {
return;
}

// Select one of the cards
if ( ! mfrc522.PICC_ReadCardSerial()) {
return;
}

// Dump debug info about the card; PICC_HaltA() is automatically called
mfrc522.PICC_DumpToSerial(&(mfrc522.uid));
}

// listen for incoming clients
EthernetClient client = server.available();
if (client) {
Serial.println("new client");
// an http request ends with a blank line
boolean currentLineIsBlank = true;
while (client.connected()) {
if (client.available()) {
char c = client.read();
Serial.write(c);
// if you've gotten to the end of the line (received a newline
// character) and the line is blank, the http request has ended,
// so you can send a reply

if (c == '\n' && currentLineIsBlank) {
// send a standard http response header
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println("Connection: close"); // the connection will be closed after completion of the response
client.println("Refresh: 5"); // refresh the page automatically every 5 sec
client.println();
client.println("");
client.println("");
// output the value of each analog input pin

client.println("");
break;
}
if (c == '\n') {
// you're starting a new line
currentLineIsBlank = true;
} else if (c != '\r') {
// you've gotten a character on the current line
currentLineIsBlank = false;
}
}}
}
// give the web browser time to receive the data
delay(100);
// close the connection:
client.stop();
Serial.println("client disconnected");
Ethernet.maintain();
}

The code you posted incorrectly does something. "It doesn't work" does not come close to providing any useful information. Describe exactly what the code does, and how that differs from what you want.

It is NOT necessary to piss away resources on the String class. NULL terminated arrays of chars and the string functions are perfectly capable of dealing with everything you are currently wasting space doing with Strings.

Calling Ethernet.maintain() on every pass through loop() is not necessary.