Unable to enter the text in the username and password fields of the Authentication pop-up window of a website using Java Robot class

Question

I am trying to automate a website using Selenium, wherein I click on the link having text as "Basic Auth". Enter the text on the username and password fields of the Authentication pop-up window using Java Robot class.

Below is the Selenium code:

        driver.get("http://the-internet.herokuapp.com/");

        driver.findElement(By.linkText("Basic Auth")).click();

        Thread.sleep(10000);

        Robot r = new Robot();

//      Move the mouse to the username field
        r.mouseMove(420, 377);
        r.mousePress(InputEvent.BUTTON1_DOWN_MASK);
        r.mouseRelease(InputEvent.BUTTON1_DOWN_MASK);

//      Enter "admin" inside the username field
        r.keyPress(KeyEvent.VK_A);
        r.keyRelease(KeyEvent.VK_A);
        r.keyPress(KeyEvent.VK_D);
        r.keyRelease(KeyEvent.VK_D);
        r.keyPress(KeyEvent.VK_M);
        r.keyRelease(KeyEvent.VK_M);
        r.keyPress(KeyEvent.VK_I);
        r.keyRelease(KeyEvent.VK_I);
        r.keyPress(KeyEvent.VK_N);
        r.keyRelease(KeyEvent.VK_N);

//      Move the mouse to the password field
        r.mouseMove(419, 404);
        r.mousePress(InputEvent.BUTTON1_DOWN_MASK);
        r.mouseRelease(InputEvent.BUTTON1_DOWN_MASK);

//      Enter "admin" inside the password field
        r.keyPress(KeyEvent.VK_A);
        r.keyRelease(KeyEvent.VK_A);
        r.keyPress(KeyEvent.VK_D);
        r.keyRelease(KeyEvent.VK_D);
        r.keyPress(KeyEvent.VK_M);
        r.keyRelease(KeyEvent.VK_M);
        r.keyPress(KeyEvent.VK_I);
        r.keyRelease(KeyEvent.VK_I);
        r.keyPress(KeyEvent.VK_N);
        r.keyRelease(KeyEvent.VK_N);

//      Press Enter key to login
        r.keyPress(KeyEvent.VK_ENTER);
        r.keyRelease(KeyEvent.VK_ENTER);

        Thread.sleep(3500);
        softassert.assertEquals(driver.findElement(By.cssSelector("h3")).getText(), "Basic Auth","Basic Auth message is not correct");
        softassert.assertEquals(driver.findElement(By.cssSelector("p")).getText(), "Congratulations! You must have the proper credentials.","Credentials message is not correct");

Output:

It is throwing below error:
<<< FAILURE!
org.openqa.selenium.WebDriverException: 
Failed to convert data to an object

It is invoking the "Authentication Required" pop-up window multiple times, instead of just once. Also, it is neither entering any text inside the username and password fields, nor clicking on the OK button.

Please help.