PowerBI Custom Connector - Windows Authentication

Dear Forum members/gurus,

Greetings, I have a query related to Windows credential/Username.

Is there anyway before sending request to the service I can retrieve Windows username and send it as a header or how the below works if I wanted to use Windows user. I wanted to send Windows user name to the my service where I can get a windows user and do further processing:

Below I have used for Windows authentication:

Sample.DataConnector = [
Authentication = [
Windows = []
],
Label = Extension.LoadString("DataSourceLabel")
];

Then I have a feed method as below, tried to use Extension.CurrentCredential but getting a null error:

Sample.DataConnector.Feed = (url as text) =>
let

Credential = Extension.CurrentCredential(),
split= Text.Split(Credential[Username],"#"),
source = Web.Contents(url, [ManualCredentials = true, Query = [
user_key = split]),
json = Json.Document(source)
in
json;

I would be really grateful if anyone can help me to resolve - In simple I wanted to send windows username from Power bi custom connector and retrieve it within my service (REST)