Trying to use https://github.com/scoop/autotask_api

sample_query.rb

#sample_query.rb
require 'autotask_api'

client = AutotaskAPI::Client.new do |c|
  c.basic_auth = ['user@example.com','mypassword']
  c.wsdl = 'https://webservices.autotask.net/atservices/1.5/atws.wsdl'
end

query = AutotaskAPI::QueryXML.new do |query|
  query.entity = 'contact'
  query.field = 'firstname'
  query.op = 'equals'
  query.expression = 'Joe'
end

client.query