Protect ajax code without Session

Question

Hi. I’m having a hard time figuring out how to protect an ajax code on my page. I have a PHP registration with a form and have a field create a username. But when the user leaves the field I check through an ajax code if the user already exists. But the ajax code is exposed in the browser console to the page that does the checking. It has how to hide this ajax or circumvent it somehow?

$("#usuario").blur(function(e){
    e.preventDefault();
    var name=$(this).val();
    $.ajax({
      type: 'POST',
      url: 'verifica_usuario.php',
      data: {
       nome:name,
      },
      success: function (response) {
          if($("#usuario").val()==""){
              $('#name_status').html("");
              $("#usuario").css("background-color","#ffffff");
              $("#enviar").attr("disabled",false);
          }else if(response=="true"){
              $('#name_status').html("Já existe esse usuário cadastrado");
              $("#usuario").css("background-color","#F6CECE");
              $("#enviar").attr("disabled",true);
          }else if(response=="false"){
              $( '#name_status' ).html("Usuário válido");
              $("#usuario").css("background-color","#CEF6D8");
              $("#enviar").attr("disabled",false);
          }
      }
  });
});