Does signing of the JWT require internet access? - oauth-2.0

Question

JWT process is to sign JWT and use JWT to retrieve an access token. This access token is used to call Google APIs.
We use Google auth library to sign JWT. IS this signing process container locally or does it require internet access to another service to sign the JWT?

Answer 1

In order to see the flow for retrieving the access token using the service account, for example, when it sees the script for retrieving the access token using Javascript, the value of jwt can be created without the web access. But, when the access token is retrieved using the jwt, it is required to access the endpoint of Google like https://www.googleapis.com/oauth2/v4/token. Ref
The script for retrieving the access token using the service account is as follows.
const private_key = "###"; // private_key of JSON file retrieved by creating Service Account
const client_email = "###"; // client_email of JSON file retrieved by creating Service Account
const scopes = ["https://www.googleapis.com/auth/drive.readonly"]; // Scopes
const url = "https://www.googleapis.com/oauth2/v4/token";
const header = { alg: "RS256", typ: "JWT" };
const now = Math.floor(Date.now() / 1000);
const claim = {
iss: client_email,
scope: scopes.join(" "),
aud: url,
exp: (now + 3600).toString(),
iat: now.toString(),
};
const signature = btoa(JSON.stringify(header)) + "." + btoa(JSON.stringify(claim));
const sign = new JSEncrypt();
sign.setPrivateKey(private_key);
const jwt = signature + "." + sign.sign(signature, CryptoJS.SHA256, "sha256");
const params = {
method: "POST",
headers: { "Content-Type": "application/json" },
body: JSON.stringify({
assertion: jwt,
grant_type: "urn:ietf:params:oauth:grant-type:jwt-bearer",
}),
};
const obj = await fetch(url, params).then((res) => res.json()).catch((err) => console.log(err));
console.log(obj);
Referencs:
Using OAuth 2.0 for Server to Server Applications
GetAccessTokenFromServiceAccount_js