findMaxCredLength.js

const keytar = require("keytar");
const SERVICE = require("os").userInfo().username;
const ACCOUNT = "VeryLongValue";

async function testCred(length) {
    const secret = '*'.repeat(length);
    try {
        await keytar.setPassword(SERVICE, ACCOUNT, secret);
    } catch {
        return false;
    }
    const newSecret = await keytar.getPassword(SERVICE, ACCOUNT);
    return newSecret.length === secret.length;
}

async function findMaxLength() {
    let length = 0;
    while (length < 1e6) {
        console.log(length);
        length += 100;
        const oldLength = length;
        while (!(await testCred(length))) {
            length--;
        }
        if (length !== oldLength) {
            return length;
        }
    }
    return length;
}

(async () => {
    const maxLength = await findMaxLength();
    console.log("Max credential length:", maxLength);
    await keytar.deletePassword(SERVICE, ACCOUNT);
})().catch((error) => {
    console.error(error);
    process.exit(1);
})