@RequestMapping(value = "/fisicHost/{id}/credentials", method = RequestMethod.GET, produces = APPLICATION_JSON_UTF8_VALUE)
public List<Credential> credentialsByFisicHost(@PathVariable(value = "id") final Long fisicHostId, ModelMap modelMap){
    FisicHost optionalFisicHost = fisicHostDao.findById(fisicHostId);

    if (optionalFisicHost == null) {
        // Responder con 404
    }
    FisicHost fisicHost = optionalFisicHost;
    return fisicHost.getCredentials();
}

<!-- Modal -->
<div class="modal fade" id="credentialsModal" tabindex="-1" role="dialog" aria-hidden="true">
    <div class="modal-dialog modal-dialog-centered" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title" id="modal-title">Credenciales</h5>
            </div>
            <div class="modal-body">
                <table id="credentialsTable">
                    <tr class="row">
                        <th id="modal-user">Usuario</th>
                        <th id="modal-pass">Clave</th>
                        <th id="modal-notes">Notas</th>
                    </tr>
                </table>
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-secondary" data-dismiss="modal">Cerrar</button>
            </div>
        </div>
    </div>
</div>

$(".credentialsButton").click(function(){

    var fisicHostId = $(this).data('fisic-host-id');
    $.get( "/fisicHost/" + fisicHostId + "/credentials", data => {
        console.log(data);

        $('#credentialsTable').empty();

//        var user = document.createElement('th');
//        user.textContent = "USUARIO";

        for (i = 0; i < data.length; ++i) {
            var fisicHost = data[i];

            var new_row = document.createElement('tr');
            new_row.className = "row fisichost";

            var userCol = document.createElement('td');
            userCol.textContent = fisicHost["user"];
            new_row.append(userCol);

            var passwordCol = document.createElement('td');
            passwordCol.textContent = fisicHost["password"];
            new_row.append(passwordCol);

            var notesCol = document.createElement('td');
            notesCol.textContent = fisicHost["notes"];
            new_row.append(notesCol);

            var editButton = document.createElement('button');
            editButton.textContent = "EDITAR"
            new_row.append(editButton);

            var deleteButton = document.createElement('button');
            deleteButton.id = buttonId;
            deleteButton.textContent = "BORRAR"
            new_row.append(deleteButton);

            $("#credentialsTable").append(new_row);

  // ACA ESTA EL TEMA

            $(deleteButton).on('click', () => {
                var credentialId = fisicHost["id"];
                console.log(credentialId);
//            $.post( "/fisicHost/" + credentialId + "/credentials", data => {});
            });
        }

        $('#credentialsModal').modal('show');

    }).fail(function(xhr, status, error) {
        console.error(error);
        alert('No se pudieron cargar las credenciales.');
    });
});

$('#credentialsModal').bind('hide', function () {
   $('#credentialsModal tr.fisichost').remove();
});

[…]
0: {…}
id: 2
notes: "notas"
password: "pass"
role: "null"
user: "usuario"
__proto__: Object { … }
1: {…}
id: 3
notes: "notasssss"
password: "pass"
role: "null"
user: "usuario"
__proto__: Object { … }
length: 2