Nodejs googleAPI how to authenticate JWT client with only GET request - node.js

Question

its known that the GoogleAPI is pretty much just built on GET requests, the helper node.js module googleapis seemingly just lets you send those GET requests in an easier way, for example:
fetch("https://www.googleapis.com/drive/v3/files/MYID/export?mimeType=text/plain",
{
method:"GET",
headers: {
'Accept-Encoding': 'gzip',
'User-Agent': 'google-api-nodejs-client/0.7.2 (gzip)',
Authorization:t.token_type +" "+ t.access_token,
Accept:"application/json"
}
})
.then(res => res.text())
.then(body => console.log(body));
accomplishes the same as using their built in method:
var drive = google.drive("v3");
drive.files.export({
auth:j,
fileId:"1oBL8sBylvODW1Md0gjXf2UgwBHtb6aRcgyGOYr0kRvY"
}, (e,r) => {
if(e) console.log(e);
else {
console.log(r,"data:::::",r.data);
}
});
So the question: When I'm validating the JWT client in nodejs using a custom service key, I do this:
var google = require("googleapis").google,
creds = require("./mycreds.json"),
fetch = require("node-fetch");
var j = new google.auth.JWT(
creds.client_email,
null,
creds.private_key,
[
"https://www.googleapis.com/auth/drive"
]
);
console.log(google.auth.JWT, "END this");
j.authorize((r,t) => {
doOther(t);
});
I suspect that this is, like every other part of the google API I've encountered so far, just an easier way to send a GET request to a certain URL with certain headers (containing the authorization key).
The question: What exactly is that URL and the headers necessary to do the same thing as j.authorize ? I couldn't find where to look in the reference.
HINT: from line 159 in jwtclient.js file:
createGToken() {
if (!this.gtoken) {
this.gtoken = new gtoken_1.GoogleToken({
iss: this.email,
sub: this.subject,
scope: this.scopes,
keyFile: this.keyFile,
key: this.key,
additionalClaims: this.additionalClaims
});
}
return this.gtoken;
}
still looking though at gtoken_1.GoogleToken etc..