Hi,
1) Is the first entered password being transferred to FreeRadius? What attributes can we use in order to obtain it? In which way is it encoded?
run FR in full debug mode eg radiusd -X , to see what is being sent to it.
3) Can we configure FreeRadius as a client of another Radius (to whom we want to redirect to) and so we can establish a secured channel through?
yes. proxying
4) The documents you refer us to are not complete. Are there any other documentation regarding FreeRadius full configuration?
everyone has their own specific requirements - some are very bespoke and such direct dedicated documents are unlikely to exist. you need to break your requirements down into their components and check each parts configuration within FreeRADIUS alan