PHP ActiveRecord, Has many with custom keys

Question

I have the following table schema ( legacy system so I can't change it :-( )

admins:
  admin_id
  ...

admin_auths:
  admin_id ( connects to admin_id )
  id ( connects to user_id )
  auth ( only care about when this is 'user' )
  ...

users:
  user_id ( connects to id )
  ...

Here is how I managed to get the relationship working for users:

User.php

class User extends ActiveRecord\Model {
    static $has_many = [
        [ 'admin_auths', 
            'foreign_key' => 'id', # key in linked table
            'primary_key' => 'user_id',  # key in "parent" (this) table
        ],
        [ 'parents',
            'through' => 'admin_auths',
            'foreign_key' => 'id', # key in linked table
            'primary_key' => 'user_id',  # key in "parent" (this) table
            'class_name' => 'Admin'
        ]
    ];
}

AdminAuth.php

class AdminAuth extends ActiveRecord\Model {
    static $belongs_to = [
        [ 'admin' ],
        [ 'user',
            'foreign_key' => 'id', # key in linked (this) table
            'primary_key' => 'user_id',  # key in "parent" table
        ]
    ];
}

If I call $user->parents or $user->admin_auths this works perfectly!

However I cannot seem to get it working in the Admin.php file:

class Admin extends ActiveRecord\Model implements JsonSerializable {
    // relationships
    static $has_many = [
        [ 'admin_auths' ],
        [ 'children',
            'through' => 'admin_auths',
            'class_name' => 'User'
        ]
    ];
    ...
}

The way it is shown above. This runs the following SQL:

SELECT `users`.* FROM `users` INNER JOIN `admin_auths` ON(`users`.user_id = `admin_auths`.user_id) WHERE `admin_id`=?

The problem with this is that I need to get it to join ON(`users`.user_id = `admin_auths`.id) ( there is no user_id column )

I've tried setting both the foreign_key and primary_key columns. foreign_key changes the where section of the query and primary_key runs no query ( Just SHOW COLUMNS on users and admin_auths ).

TL;DR: How to I customize the join on a PHP ActiveRecord has_many association?