See that line on the page:
Add Authorized redirect URIs end enter https://my.home-assistant.io/redirect/oauth
Basically on Mercedes console side you need to put callback to your Home-Assistant instance (needs to be public accessible and probably on https), and it will return token to you.
Why not to implement a proper oauth flow? Home-Assistant has this ability. I've recently set up Nest component: https://www.home-assistant.io/integrations/nest/
See that line on the page:
Add Authorized redirect URIs end enter https://my.home-assistant.io/redirect/oauthBasically on Mercedes console side you need to put callback to your Home-Assistant instance (needs to be public accessible and probably on https), and it will return token to you.
BTW, for some reason URI for me should be https://my.home-assistant.io/auth/external/callback, and not like in documentation.