What is the nature and description of the request?

Make the user search case-insensitive. Currently, if I have the following users

• user1
• User2
• user3

and I search for "user", only user1 and user3 will be returned. Ideally, all 3 users would be returned.

Why does the customer need this? (List the business requirements here)

When auditing users, it's possible that some users may be unknowingly excluded from search results if their username does not match the pattern exactly. 

How would you like to achieve this? (List the functional requirements here)

use "icontains" instead of "contains" when searching for users by default. You may want to allow for "contains" to be selected as an alternative.