Si desea permitir el inicio de sesion de dirección de correo electrónico pero no con el nombre de usuario
En tu inc/functions_user.php busca:

/**
 * Checks a password with a supplied username.
 *
 * @param string The username of the user.
 * @param string The plain-text password.
 * @return boolean|array False when no match, array with user info when match.
 */
function validate_password_from_username($username, $password)
{
	global $db;

	$query = $db->simple_select("users", "uid,username,password,salt,loginkey,coppauser,usergroup", "LOWER(username)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

	$user = $db->fetch_array($query);
	if(!$user['uid'])
	{
		return false;
	}
	else
	{
		return validate_password_from_uid($user['uid'], $password, $user);
	}
}

Y cambia por:

/**
 * Checks a password with a supplied username.
 *
 * @param string The username of the user.
 * @param string The plain-text password.
 * @return boolean|array False when no match, array with user info when match.
 */
function validate_password_from_username($username, $password)
{
	global $db;

	$query = $db->simple_select("users", "uid,username,email,password,salt,loginkey,coppauser,usergroup", "LOWER(email)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

	$user = $db->fetch_array($query);
	if(!$user['uid'])
	{
		return false;
	}
	else
	{
		return validate_password_from_uid($user['uid'], $password, $user);
	}
}

Si quieres permitir iniciar sesión con el nombre de usuario o dirección de correo electrónico
En tu inc/functions_user.php busca:

/**
 * Checks a password with a supplied username.
 *
 * @param string The username of the user.
 * @param string The plain-text password.
 * @return boolean|array False when no match, array with user info when match.
 */
function validate_password_from_username($username, $password)
{
	global $db;

	$query = $db->simple_select("users", "uid,username,password,salt,loginkey,coppauser,usergroup", "LOWER(username)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

	$user = $db->fetch_array($query);
	if(!$user['uid'])
	{
		return false;
	}
	else
	{
		return validate_password_from_uid($user['uid'], $password, $user);
	}
}

Y cambia por:

/**
 * Checks a password with a supplied username.
 *
 * @param string The username of the user.
 * @param string The plain-text password.
 * @return boolean|array False when no match, array with user info when match.
 */
function validate_password_from_username($username, $password)
{
	global $db;

	$query = $db->simple_select("users", "uid,username,email,password,salt,loginkey,coppauser,usergroup", "LOWER(username)='".$db->escape_string(my_strtolower($username))."' OR LOWER(email)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

	$user = $db->fetch_array($query);
	if(!$user['uid'])
	{
		return false;
	}
	else
	{
		return validate_password_from_uid($user['uid'], $password, $user);
	}
}

Para ambas
En tu inc/functions_user.php busca:

/**
 * Checks if $username already exists in the database.
 *
 * @param string The username for check for.
 * @return boolean True when exists, false when not.
 */
function username_exists($username)
{
        global $db;

        $query = $db->simple_select("users", "COUNT(*) as user", "LOWER(username)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

        if($db->fetch_field($query, 'user') == 1)
        {
                return true;
        }
        else
        {   
                return false;
        }
}

Y cambia por:

/**
 * Checks if $username already exists in the database.
 *
 * @param string The username for check for.
 * @return boolean True when exists, false when not.
 */
function username_exists($username)
{
	global $db;

	$query = $db->simple_select("users", "COUNT(*) as user,email,username", "LOWER(username)='".$db->escape_string(my_strtolower($username))."' OR LOWER(email)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

	if($db->fetch_field($query, 'user') == 1)
	{
		return true;
	}
	else
	{
		return false;
	}
}

Creditos: Dylan M.

Espectacular

Muchas gracias por traerlo Dani. Rep+

cool!
el de ambas esta genial!
Gracias Dano ;D

Awesome!! Gracias por compartir con todos nosotros.

Yo lo probé y no funciono...

Cuando realizas el paso 1 "o" 2 es opcional (uno solo de los 2) y el 3ro es para ambas

Yo utilize este paso..

Para ambas
En tu inc/functions_user.php busca:

/**
 * Checks if $username already exists in the database.
 *
 * @param string The username for check for.
 * @return boolean True when exists, false when not.
 */
function username_exists($username)
{
        global $db;

        $query = $db->simple_select("users", "COUNT(*) as user", "LOWER(username)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

        if($db->fetch_field($query, 'user') == 1)
        {
                return true;
        }
        else
        {   
                return false;
        }
}

Y cambia por:

/**
 * Checks if $username already exists in the database.
 *
 * @param string The username for check for.
 * @return boolean True when exists, false when not.
 */
function username_exists($username)
{
	global $db;

	$query = $db->simple_select("users", "COUNT(*) as user,email,username", "LOWER(username)='".$db->escape_string(my_strtolower($username))."' OR LOWER(email)='".$db->escape_string(my_strtolower($username))."'", array('limit' => 1));

	if($db->fetch_field($query, 'user') == 1)
	{
		return true;
	}
	else
	{
		return false;
	}
}

Ya que quiero que se pueda Iniciar Sesion tanto con su Correo como con su Nombre de Usuario, pero no me funciona... O estoy utilizando el Equivocado..??

Excelente tutorial, +1.

Infraworld ocupas usar esa + la segunda

Infraworld ocupas usar esa + la segunda

Gracias Amigo, Me Funciono Perfecto.. +1Rep.