public RadiusAuthenticationProtocol getRadiusEAPTTLSInnerProtocol()
            throws GuacamoleException {
        
        RadiusAuthenticationProtocol authProtocol = environment.getRequiredProperty(
            RadiusGuacamoleProperties.RADIUS_EAP_TTLS_INNER_PROTOCOL
        );
        
        if (authProtocol == RadiusAuthenticationProtocol.EAP_TTLS)
            throw new GuacamoleServerException("Invalid inner protocol specified for EAP-TTLS.");
        
        return authProtocol;
        
    }
Returns the tunneled protocol that RADIUS should use
when the authentication protocol is set to EAP-TTLS, as
configured in the guacamole.properties file.

@return
    The tunneled protocol that should be used inside
    an EAP-TTLS RADIUS connection. 
    
@throws GuacamoleException
    If guacamole.properties cannot be parsed, or if EAP-TTLS is specified
    as the inner protocol.
extensions/guacamole-auth-radius/src/main/java/org/apache/guacamole/auth/radius/conf/ConfigurationService.java