public String getClientId() throws GuacamoleException {
        return environment.getRequiredProperty(DUO_CLIENT_ID);
    }
Returns the Duo client id received from Duo for verifying Guacamole
users, as defined in guacamole.properties by the "duo-client-id"
property. This value MUST be exactly 20 characters.

@return
    The client id received from Duo for verifying Guacamole users.

@throws GuacamoleException
    If the associated property within guacamole.properties is missing.
extensions/guacamole-auth-duo/src/main/java/org/apache/guacamole/auth/duo/conf/ConfigurationService.java