Integrate directory services into custom ticket field

Feature Request Summary: 

Zendesk should create a custom field type that is a "User Lookup", that could work from either existing Zendesk users, or to those associated with a directory service (Active Directory, Okta, etc). Bonus: Allow these fields to be filtered based on a passed-through attribute (like department, title, group, etc.)

By extension, any "lookup field" that could reference a database or other source-of-truth would be ideal. 

Description/Use Cases: 

Certain workflows could be improved by having a "user lookup" utility. For example, if there is a ticket form where a user requests equipment, and such a request needs to be approved by their manager, this field could reduce the amount of overhead and circuitous API work performed by agents or Zendesk admins. Additionally, it would improve the experience of adding CC's to a ticket, insofar that users could auto-populate. 

Another use case is where we have internal forms that someone may complete on behalf of multiple users, such as requesting changes to multiple team members in the org at once. Currently, we have to use REGEX to ensure that email fields are true to the org, or have to hope that data entered into free text fields is valid. This would ensure data integrity and simplify the experience of switching between systems to enter email addresses, etc.

Business impact of limitation or missing feature:

This is a feature improvement; such a feature would reduce friction and potential errors from end users when completing forms, and would integrate an otherwise manual process directly inside Zendesk.

Other necessary information or resources:

Similar solutions exist for products like Jira Service Desk (albeit through extension): https://scriptrunner.adaptavist.com/latest/jira/script-fields/ldap-picker.html

Also available on Freshservice: https://support.freshservice.com/support/solutions/articles/50000001060-add-a-lookup-field-to-a-service-item-form