Support current AVM Authentication method

[MatthiasFraass]

On my Fritzbox 7530AX, I suddenly get login errors with fritzbox_smarthome_exporter.
I am highly interested in getting fritzbox_smarthome_exporter to work again, as a lot of smart devices are AVM products.

I suspect it has to do with the upgrade to FritzOS 8.0 - from the day on that the update was installed, I only get:
"Login failed: unable to solve login challenge: challenge not solved, got '0000000000000000' as session id, check login data"

Diving deeper, it seems that AVM has introduced a new method and seems to discontinue the old one (I suspect).
See https://avm.de/fileadmin/user_upload/Global/Service/Schnittstellen/AVM_Technical_Note_-_Session_ID_english_2021-05-03.pdf

The underlying fritzctl only supports the older MD5 login method, not PBKDF2/HMac.
bpicode/fritzctl seems to have been discontinued, so I guess that's why you are using a fork.

So I went a little deeper and developed a prototype for a PBKDF2-based challenge/response login method working in golang. I can successfully login with it and obtain a valid SID.
It should work with any Fritzbox > 7.24 which should be good for everyone at this time.

As GoLang is not my first language, I have a bit of trouble integrating it into fritzctl.
I could try a fork but it would take a while for me to integrate it with fritzbox_smarthome_exporter.

What can we do about it?

[MatthiasFraass]

I created a working new version :)
https://github.com/MatthiasFraass/fritzctl

You have to do 3 things to get it working:

• add it as a "replace" in go.mod
• use parameter -url="https://fritz.box/login_sid.lua?version=2"
• modify main.go so it supports not only the hostname but also a URI,
  insert somewhere around line 129:

	if fbURL.RequestURI() != "/" {
		options = append(options, fritz.AuthEndpoint(fbURL.RequestURI()))
	}

Maybe I do a clean fork tomorrow, but so far it's working :)