Safely inject credentials in HTTP headers with Vercel Sandbox
By Steven Van ·
Vercel Sandbox can inject API keys into outbound request headers so sandboxed code never sees the credentials itself.
Vercel Sandbox can now inject HTTP headers into outbound requests made by sandboxed code, so API keys and tokens stay outside the sandbox VM. Code running inside the sandbox can call authenticated services like AI Gateway or GitHub without ever having access to the credential itself.
Header injection is set up as a transform rule in the sandbox's network policy: when the sandbox makes an HTTPS request to a matching domain, the firewall adds or replaces the specified headers before forwarding the request. It works alongside any egress configuration, including policies that allow general internet access while injecting credentials only for specific domains. Vercel positions this for AI agent workflows where prompt injection is a risk: even if an agent is compromised, there is nothing inside the sandbox to exfiltrate.
Injection rules can also be updated on a running sandbox without a restart, which Vercel says supports multi-phase workflows, for example injecting credentials to clone repositories during setup, then removing them before running untrusted code. Full details are in the sandbox firewall documentation.