// When pressed the button, selects the "username" Textfield.
var username : String = "username";
var pwd : String = "a pwd";
function OnGUI () {
    // Set the internal name of the textfield
    GUI.SetNextControlName ("MyTextField");
    
    // Make the actual text field.
    username = GUI.TextField (Rect (10,10,100,20), username);
    pwd = GUI.TextField (Rect (10,40,100,20), pwd);

    // If the user presses this button, keyboard focus will move.
    if (GUI.Button (Rect (10,70,80,20), "Move Focus"))
        GUI.FocusControl ("MyTextField");    
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public string username = "username";
    public string pwd = "a pwd";
    void OnGUI() {
        GUI.SetNextControlName("MyTextField");
        username = GUI.TextField(new Rect(10, 10, 100, 20), username);
        pwd = GUI.TextField(new Rect(10, 40, 100, 20), pwd);
        if (GUI.Button(new Rect(10, 70, 80, 20), "Move Focus"))
            GUI.FocusControl("MyTextField");
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public username as string = 'username'

    public pwd as string = 'a pwd'

    def OnGUI():
        GUI.SetNextControlName('MyTextField')
        username = GUI.TextField(Rect(10, 10, 100, 20), username)
        pwd = GUI.TextField(Rect(10, 40, 100, 20), pwd)
        if GUI.Button(Rect(10, 70, 80, 20), 'Move Focus'):
            GUI.FocusControl('MyTextField')