Section 3.94.1. Hostname, SecretKey and IntegrationKey
Section 3.94.2. DefaultFactor(1159 / 1693)
Section 3.94.3. PreAuth
3.94.2. DefaultFactor
If the user does not specify a valid password or factor, this
will be the factor requested from Duo. May be one of "push", "sms",
"phone", "auto". Defaults to "auto".