HttpContext.Current is null in custom SecurityEntityProvider

Description

Steps to reproduce

1. Create a custom SecurityEntityProvider that calls the HttpContext.Current in the Search method.
2. In the edit page, click Edit Approval Sequence.
3. Enable an approval sequence and enter the reviewer's name.

Expected: You get the reviewer's name in the reviewer drop down.

Actual: NullReferenceException in the custom SecurityEntityProvider created in step 1.