How to get username when using PKI authentication?

[bungder]

When using PKI authenication, codes are like this:

AuthClient authClient = new AuthClient("username", "clientId", "privateKey");
String accessToken = authClient.getAccessToken();

In ZoomInfo API doc, I should do these few actions to get the necessary parameters:

1. Log in to the ZoomInfo GUI using admin credentials with API access.
2. Go to Admin Portal > API and click Generate New Key. You are provided with a Client ID and a Private Key.
3. Import a public library that authenticates using this Client ID and Private Key and generates a JWT.

username is not mentioned in the above steps. How can I get this username?