How to query for a specific username in the admin API

In the Admin documentation, there is python code used to generate the authentication and date headers. I have it working to show for all usernames but when i want to add a parameter of “username=administrator” but no matter how i put it in, i get an error 40103 about the signature. The documentation provides no example of how to place in the parameter. Has anyone got it working and could show me an example? thank you