Read HTTP request headers, and modify response headers of an Apps Script web app
google-apps-script
Solution
You cannot read or set HTTP Headers in a Apps Script app deployed as a web app. You are restricted to reading the query string or the post values for GET/POST respectively. When responding you can only return the content and the MIME type (restricted to a few types)
This is because the scripts are served off the Google.com domain and you should not have ways to set/get cookies that could potentially be used for malicious reasons.
However, if you are using UrlFetch within an Apps Script app to make outbound calls, you have much more control of the HTTP headers
Problem
Can I modify the HTTP response headers to add cookies and extra information? Also I'm having troubles reading the request headers.