WebHelp Desk REST API

I would like to use REST API to fetch client tickets or other information. Also functionality to create tickets through web-services. How can i autheticate the client user and get tickets for the current client while passing client email for example kanwargrewal@gmail in the GET POST request?

For example fetching request types for client having email kanwargrewal@gmail.com

https://whd.mulkeyinc.com/helpdesk/WebObjects/Helpdesk.woa/ra/RequestTypes?apiKey=m6af2xR48aH6epw6PCZ0tQCJgnTbFiVz5y6aln…

It is giving error as Authentication required.

Please help.

Thanks

Kanwar