client-python

python-fido2 Extension

In order to implement support for an extension in the python-fido2 library by Yubico, some changes to the source code have to be done. The process is straigt forward and only requires modification of a single file.

In fido2/ctap2/extensions.py, create a new subclass of Ctap2Extension. There are two important Methods that need to be overidded.

• process_create_input that controls which input data is passed to the authenticator by data that is received from a relying party
• process_create_output that parses the received return data from the authenticator in order to forward it to a relying party

There is no need to register this class anywhere as all subclasses of Ctap2Extension in the library are automatically detected.

The greeter extension for example looks like this

class GreeterExtension(Ctap2Extension):
    """
    Implements the greeter CTAP2 extension
    """

    NAME = "greeter"

    def process_create_input(self, inputs):
        return self.is_supported() and inputs.get(self.NAME):

    def process_create_output(self, auth_data):
        if self.NAME in auth_data.extensions:
            return {"greeter": auth_data.extensions.get(self.NAME)}