SSH: Execute different shell based on public key used

I want to allow ssh access to a specific account, but if I connect using a specific puclic key, I should be dropped to a full shell, otherwise to a restricted one.

Example:

I connect with ssh to [email protected] using the public key ABCDEF (correctly set up in authorized_keys) and I get a /bin/zsh shell

If I connect to [email protected] with a password or another public key, I get a /bin/rsh shell

My idea was to create a custom intermediate shell (IE: /bin/mysh), check the key used and execute the correct shell from there, but I don't know how to check which key was used (or if it's possible at all).

env doesn't seem to contain anything useful.

Any ideas on how to do this or other possible solutions?

Thanks.