In the Main menu choose Users.
On the form that opens, select the user to whom you want to grant access to the module, and click the Edit button
In the opened user settings, go to the Access section and enable the checkbox next to Can use PHP Composer, click the Save button.
Also, when creating a new user, it is possible to immediately grant access to PHP Composer by marking the corresponding checkbox in the Access section.
To turn off, unmark the checkbox Can use PHP Composer, as described in the Enabling section.