The joomla/ldap package is deprecated with no future updates planned.
Add "joomla/ldap": "~2.0" to the require block in your composer.json and then run composer install.
{
"require": {
"joomla/ldap": "~2.0"
}
}Alternatively, you can simply run the following from the command line:
composer require joomla/ldap "~2.0"