Sample config values:
verify_uri 'http://captcha.servicoscorporativos.serpro.gov.br/captchavalidar/1.0.0/validar'
serpro_client_id 'fdbcdc7a0b754ee7ae9d865fda740f17'
See http://stdcs.supst.serpro/manual/html/#captcha/page/introducao.html for more details.