Q: What does “Could not download page (407)” mean? A: A 407 error means your request reached a proxy that blocked it because it requires authentication, and the proxy responds with a Proxy-Authenticate header specifying a scheme like Basic, NTLM, or Negotiate. This HTTP 407 proxy authentication guide explains that your client must send a matching Proxy-Authorization header to proceed. Q: How can I confirm whether I’m behind a proxy? A: Check system and browser proxy settings, PAC scripts, and environment variables like HTTP_PROXY or HTTPS_PROXY, and inspect files such as /etc/environment or shell profiles. You can also run curl -I http://example.com without and with the proxy; if the proxied request returns HTTP/1.1 407 you have confirmed the proxy is enforcing authentication. Q: How do I add proxy credentials for command-line tools like curl, git, or npm? A: Supply valid credentials in the tool’s proxy settings or environment variables—for example curl -x http://user:pass@proxy.company.com:8080, git config –global http.proxy http://user:pass@proxy:8080, or npm config set proxy http://user:pass@proxy:8080. The HTTP 407 proxy authentication guide also recommends URL-encoding special characters and preferring environment variables or secure config files over hardcoding. Q: What should I do if I still get 407 after entering credentials? A: Remove stale or duplicate proxy settings, unset conflicting HTTP(S)_PROXY variables, restart the app or service, and verify your client supports the proxy auth scheme (NTLM or Negotiate) that the proxy advertises. If SSL inspection is involved, install the corporate root certificate and ask the network team to allowlist the target if traffic remains blocked. Q: Why do browsers sometimes fail with “Proxy Authentication Required” and how do I fix it? A: Ensure the proxy is set only once and remove any leftover PAC script when switching to a manual proxy, then enter the correct domain credentials using DOMAINuser if required. If HTTPS pages fail after sign-in, install the corporate root certificate to avoid SSL inspection issues. Q: How do I fix 407 errors in CI/CD or remote build pipelines? A: Add proxy variables in the runner or pipeline secret store and run a simple test step like curl -I to confirm you get a non-407 status after authentication. Ensure credentials are stored securely and that build agents have the proper proxy settings loaded. Q: What are safe practices for storing and handling proxy credentials? A: Do not commit proxy credentials to Git and use environment variables, secret stores, or OS keychains instead, and rotate passwords or tokens on schedule. The HTTP 407 proxy authentication guide also advises preferring HTTPS proxies to protect logins and setting NO_PROXY for internal hosts. Q: What quick troubleshooting checklist should I run before contacting the network admin? A: Confirm you are actually behind a proxy, verify proxy host, port, and scheme and that credentials match the required auth scheme, unset old HTTP(S)_PROXY variables, restart your app, and test with a simple curl -I via the proxy to look for a non-407 response. If problems persist, capture the proxy response headers as the HTTP 407 proxy authentication guide suggests and share them with your network admin.