public List<IPAddress> getEnforceHosts() throws GuacamoleException {
        return environment.getProperty(DUO_ENFORCE_HOSTS, Collections.emptyList());
    }
Returns the list of IP addresses and subnets defined in guacamole.properties
for which Duo MFA should explicitly be enforced, while logins from all
other hosts should not enforce MFA. Users logging in from hosts
contained in this list will be required to complete the Duo MFA authentication,
while users from all other hosts will be logged in without the MFA requirement.

@return
    A list of IP addresses and subnets for which Duo MFA should be
    explicitly enforced.

@throws GuacamoleException 
    If guacamole.properties cannot be parsed, or if an invalid IP address
    or subnet is specified.
extensions/guacamole-auth-duo/src/main/java/org/apache/guacamole/auth/duo/conf/ConfigurationService.java