How to configure proxy in Web Test tool?

curl-loader
    Syntax to be used:
  1. PROXY_AUTH_METHOD to be configured from the "BASIC", "DIGEST", "GSS_NEGOTIATE", "NTLM" or "ANY".
  2. PROXY_AUTH_CREDENTIALS to be provided in the form "user:password". If not configured, the loader uses USERNAME and PASSWORD tags value to synthesize the credentials.
How to configure proxy in Web Test Tool?