in lib/aws/session_store/dynamo_db/configuration.rb [219:226]
def env_options
default_options.keys.inject({}) do |opts, opt_name|
env_var = "DYNAMO_DB_SESSION_#{opt_name.to_s.upcase}"
opts[opt_name] = ENV[env_var] if ENV.key?(env_var)
opts
end
end