O365 Site Collection Users List

Recently I was in a need to get a list of all the users from a list of O365 Site Collections and I thought of following approaches to do this:

Approach 1:

1. Get a list of site collections in a CSV
2. Loop through them one by one
3. From each site collection get a list of groups
   and download users in it
4. There will be other users added directly to the
   site collection. In that case get the user from each web directly.

But there are many gotchas with
this approach:

1. What if user has broken permissions to a page or
   library and added user(s) directly to that?
2. Same goes with a subsite

Approach 2:

1. We know that every site collection has a User
   Information List, which is hidden
2. You can access it appending ‘/_catalogs/users/simple.aspx’
   to your site collection
3. Every user added to the site collection, no matter
   where, it will go and sit in the User Information List at the Site Collection
   level
4. Simplistically thinking the User Information List
   is just another SharePoint list. You can access it using the Web object as Web.SiteUserInfoList

Therefore, approach 2 seemed more appropriate and can be
achieved in quick time. You can access the code here.