REST API - Get username using email address

[Steve Phillips]

We have a need to disable users when they leave the organization.  Since 8.2 the REST API has the ability to disable a user by username. I have tested it and it works great.

The notifications we receive when a person leaves the organization contain the email address. 

We need to be able to get the username using the email address.

This is possible in Jira but does not seem to be possible in Confluence.

Is there a way to get the username using the email address?  Even if it is multiple steps I am OK with that. 

TIA

Steve