jwks_client.py

import json
import urllib.request
from functools import lru_cache
from typing import Any, List, Optional
from urllib.error import URLError

from .api_jwk import PyJWK, PyJWKSet
from .api_jwt import decode_complete as decode_token
from .exceptions import PyJWKClientError
from .jwk_set_cache import JWKSetCache


class PyJWKClient:
    def __init__(
        self,
        uri: str,
        cache_keys: bool = False,
        max_cached_keys: int = 16,
        cache_jwk_set: bool = True,
        lifespan: int = 300,
    ):
        self.uri = uri
        self.jwk_set_cache: Optional[JWKSetCache] = None

        if cache_jwk_set:
            # Init jwt set cache with default or given lifespan.
            # Default lifespan is 300 seconds (5 minutes).
            if lifespan <= 0:
                raise PyJWKClientError(
                    f'Lifespan must be greater than 0, the input is "{lifespan}"'
                )
            self.jwk_set_cache = JWKSetCache(lifespan)
        else:
            self.jwk_set_cache = None

        if cache_keys:
            # Cache signing keys
            # Ignore mypy (https://github.com/python/mypy/issues/2427)
            self.get_signing_key = lru_cache(maxsize=max_cached_keys)(self.get_signing_key)  # type: ignore

    def fetch_data(self) -> Any:
        jwk_set: Any = None
        try:
            with urllib.request.urlopen(self.uri) as response:
                jwk_set = json.load(response)
        except URLError as e:
            raise PyJWKClientError(f'Fail to fetch data from the url, err: "{e}"')
        else:
            return jwk_set
        finally:
            if self.jwk_set_cache is not None:
                self.jwk_set_cache.put(jwk_set)

    def get_jwk_set(self, refresh: bool = False) -> PyJWKSet:
        data = None
        if self.jwk_set_cache is not None and not refresh:
            data = self.jwk_set_cache.get()

        if data is None:
            data = self.fetch_data()

        return PyJWKSet.from_dict(data)

    def get_signing_keys(self, refresh: bool = False) -> List[PyJWK]:
        jwk_set = self.get_jwk_set(refresh)
        signing_keys = [
            jwk_set_key
            for jwk_set_key in jwk_set.keys
            if jwk_set_key.public_key_use in ["sig", None] and jwk_set_key.key_id
        ]

        if not signing_keys:
            raise PyJWKClientError("The JWKS endpoint did not contain any signing keys")

        return signing_keys

    def get_signing_key(self, kid: str) -> PyJWK:
        signing_keys = self.get_signing_keys()
        signing_key = self.match_kid(signing_keys, kid)

        if not signing_key:
            # If no matching signing key from the jwk set, refresh the jwk set and try again.
            signing_keys = self.get_signing_keys(refresh=True)
            signing_key = self.match_kid(signing_keys, kid)

            if not signing_key:
                raise PyJWKClientError(
                    f'Unable to find a signing key that matches: "{kid}"'
                )

        return signing_key

    def get_signing_key_from_jwt(self, token: str) -> PyJWK:
        unverified = decode_token(token, options={"verify_signature": False})
        header = unverified["header"]
        return self.get_signing_key(header.get("kid"))

    @staticmethod
    def match_kid(signing_keys: List[PyJWK], kid: str) -> Optional[PyJWK]:
        signing_key = None

        for key in signing_keys:
            if key.key_id == kid:
                signing_key = key
                break

        return signing_key