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import abc |
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import os |
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import struct |
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import subprocess |
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from google.auth import exceptions |
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from google.oauth2.webauthn_types import GetRequest, GetResponse |
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class WebAuthnHandler(abc.ABC): |
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@abc.abstractmethod |
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def is_available(self) -> bool: |
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"""Check whether this WebAuthn handler is available""" |
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raise NotImplementedError("is_available method must be implemented") |
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@abc.abstractmethod |
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def get(self, get_request: GetRequest) -> GetResponse: |
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"""WebAuthn get (assertion)""" |
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raise NotImplementedError("get method must be implemented") |
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class PluginHandler(WebAuthnHandler): |
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"""Offloads WebAuthn get reqeust to a pluggable command-line tool. |
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Offloads WebAuthn get to a plugin which takes the form of a |
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command-line tool. The command-line tool is configurable via the |
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PluginHandler._ENV_VAR environment variable. |
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The WebAuthn plugin should implement the following interface: |
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Communication occurs over stdin/stdout, and messages are both sent and |
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received in the form: |
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[4 bytes - payload size (little-endian)][variable bytes - json payload] |
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""" |
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_ENV_VAR = "GOOGLE_AUTH_WEBAUTHN_PLUGIN" |
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def is_available(self) -> bool: |
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try: |
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self._find_plugin() |
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except Exception: |
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return False |
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else: |
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return True |
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def get(self, get_request: GetRequest) -> GetResponse: |
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request_json = get_request.to_json() |
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cmd = self._find_plugin() |
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response_json = self._call_plugin(cmd, request_json) |
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return GetResponse.from_json(response_json) |
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def _call_plugin(self, cmd: str, input_json: str) -> str: |
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input_length = len(input_json) |
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length_bytes_le = struct.pack("<I", input_length) |
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request = length_bytes_le + input_json.encode() |
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process_result = subprocess.run( |
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[cmd], input=request, capture_output=True, check=True |
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) |
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response_len_le = process_result.stdout[:4] |
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response_len = struct.unpack("<I", response_len_le)[0] |
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response = process_result.stdout[4:] |
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if response_len != len(response): |
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raise exceptions.MalformedError( |
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"Plugin response length {} does not match data {}".format( |
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response_len, len(response) |
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) |
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) |
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return response.decode() |
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def _find_plugin(self) -> str: |
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plugin_cmd = os.environ.get(PluginHandler._ENV_VAR) |
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if plugin_cmd is None: |
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raise exceptions.InvalidResource( |
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"{} env var is not set".format(PluginHandler._ENV_VAR) |
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) |
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return plugin_cmd |
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