File content as of revision 2:1ffd9e2ce7df:

#include "mbed.h"
#include "EthernetInterface.h"
#include "HTTPClient.h"

DigitalOut R(PTB22);                  // PTB22 = Red   pin
DigitalOut G(PTE26);                  // PTE26 = Green pin
DigitalOut B(PTB21);                  // PTB21 = Blue  pin

Serial serial(USBTX, USBRX); // tx, rx
EthernetInterface eth;
HTTPClient http;
char str[8192];

int main() {
    setbuf(stdout, NULL);
    eth.init(); //Use DHCP
    eth.connect();
    http.dumpResHeader(true);

    while(1){
        // Wait for Token on Serial and read to str
        while(1){
               if(serial.readable()){
                    serial.scanf("%s",&str);
                    break;
                }
        }
        printf(str);
        
        // Send token to Server
        // POST date, more examples on https://developer.mbed.org/users/donatien/code/HTTPClient_HelloWorld/file/270e2d0bb85a/main.cpp
        printf("\nTrying to fetch page...\n");
        HTTPMap map;
        HTTPText inText(str, 512);
        map.put("Hello", "World");
        map.put("test", "1234");
        printf("\nTrying to post data...\n");
        int ret = http.post("http://httpbin.org/post", map, &inText);    
        if (!ret)
        {
          printf("Page fetched successfully - read %d characters\n", strlen(str));
          printf("Result: %s\n", str);
          // Unlock
          R=!R;
          wait(1);
          R=!R;
        }
        else
        {
          printf("Error - ret = %d - HTTP return code = %d\n", ret, http.getHTTPResponseCode());
        }
    }
    
    eth.disconnect();  
}