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HTTP 407 Proxy Authentication — Corporate Proxy Authorization Failures

Warning4xx client error

Overview

Fix HTTP 407 Proxy Authentication Required errors in corporate environments where proxy servers require credentials for internet access.

Key Details

  • HTTP 407 indicates the client must authenticate with the proxy server before the request is forwarded
  • Corporate proxy servers commonly require domain credentials (NTLM, Kerberos, or Basic authentication)
  • The proxy responds with Proxy-Authenticate header indicating the supported authentication schemes
  • CLI tools, Docker, npm, pip, and git often fail behind corporate proxies without explicit configuration
  • Proxy auto-configuration (PAC) files may route different URLs through different proxy servers

Common Causes

  • HTTP_PROXY/HTTPS_PROXY environment variables not set for command-line tools
  • Proxy credentials expired or changed since last configuration
  • Tool not supporting the proxy authentication scheme (e.g., NTLM not supported by basic HTTP clients)
  • PAC file routing requests to a different proxy than configured

Steps

  1. 1Set proxy environment variables: export HTTP_PROXY=http://user:pass@proxy:8080 and HTTPS_PROXY similarly
  2. 2Configure git: 'git config --global http.proxy http://user:pass@proxy:8080'
  3. 3Configure npm: 'npm config set proxy http://user:pass@proxy:8080' and 'npm config set https-proxy'
  4. 4For NTLM proxies, use CNTLM or Px as a local proxy that handles NTLM authentication transparently
  5. 5Check proxy settings in system preferences and ensure CLI tools pick them up

Tags

proxy407authenticationcorporatentlm

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Frequently Asked Questions

Check System Preferences > Network > Advanced > Proxies on Mac, or Settings > Network > Proxy on Windows. Corporate IT may also provide a PAC file URL.