auth.js

const crypto = require('crypto');
const url = require('url');

function getHeaders(method, fullUrl, accessKey, secretKey) {
    const urlObj = url.parse(fullUrl);
    const urlPath = urlObj.pathname;
    const urlQuery = urlObj.query ? urlObj.query : '';
    
    const authDate = new Date().toUTCString();
    const nonce = crypto.randomBytes(25).toString('base64').substring(0, 25);
    const contentType = 'application/json';
    
    // Build the string to sign according to Onshape's format
    const stringToSign = (
        method + '\n' +
        nonce + '\n' +
        authDate + '\n' +
        contentType + '\n' +
        urlPath + '\n' +
        urlQuery + '\n'
    ).toLowerCase();
    
    const hmac = crypto.createHmac('sha256', secretKey)
        .update(stringToSign)
        .digest('base64');
    
    const signature = 'On ' + accessKey + ':HmacSHA256:' + hmac;
    
    return {
        'Authorization': signature,
        'Date': authDate,
        'On-Nonce': nonce,
        'Content-Type': contentType
    };
}

module.exports = { getHeaders };