General propose: deactivate, block and delete inactive Gitlab users.

• Create full backup your existing Gitlab installation before run script!
• Copy script into /var/opt/gitlab/.rake (create if it doesn't exist).
• Check variable excluded_users and excluded_by_mask for excluding some users. Bot's will be excluded automatically.
• Check log_file_path for script logging, user must have sufficient privileges.
• Console run: in terminal gitlab-rake -R /var/opt/gitlab/.rake/ mycompany:block_inactive_users BLOCK=true
• Cron schediling: 0 0 * * 0 /usr/bin/gitlab-rake -R /var/opt/gitlab/.rake/ mycompany:block_inactive_users BLOCK=true
• After script complete, check log file for detailed info.

If BLOCK flag doesn't exist or not set to true script running in dry-run mode (i.e. no deletion/blocking/deactivating user accounts).

• https://docs.gitlab.com/ee/user/admin_area/activating_deactivating_users.html
• https://docs.gitlab.com/ee/user/admin_area/blocking_unblocking_users.html
• https://docs.gitlab.com/ee/user/profile/account/delete_account.html

• https://docs.gitlab.com/ee/administration/auth/ldap/#user-sync

• Fill excluded_users (users and bots) and excluded_by_mask
• Step 1. Delete blocked users without Projects and last activity more than 90 days
• Step 2. Block deactivated users with last activity more than 60 days
• Step 3. Deactivate users with last activity (last_activity_on) is nil or more than 35 days

• Send report by E-mail

• Message "WARNING: Active Record does not support composite primary key. Project_authorizations has composite primary key. Composite primary key is ignored". Has no effect for script, fixed in Gitlab 13.9.