Add a fix to the error raised when using empty spiffeID in fetch_jwt_…

[telliere]

…svid

Modifying this part :

    @handle_error(error_cls=FetchJwtSvidError)
    def fetch_jwt_svid(
        self, audiences: List[str], subject: Optional[SpiffeId] = None
    ) -> JwtSvid:
        if not audiences:
            raise ArgumentError('Parameter audiences cannot be empty')
       
        response = self._spiffe_workload_api_stub.FetchJWTSVID(
            request=workload_pb2.JWTSVIDRequest(
                audience=audiences,
                spiffe_id=str(subject),
            )
        )

        if len(response.svids) == 0:
            raise FetchJwtSvidError('JWT SVID response is empty')

        svid = response.svids[0].svid
        return JwtSvid.parse_insecure(svid, audiences)

Bug :

When using fetch_jwt_svid with no spiffeID specified it raises a FetchJwtSvidError while it shouldn't.

Cause :

spiffe_id=str(subject),

parsing a None object as a str creates 'None', causing the next function (JWTSVIDRequest) to consider having a specified spiffeID when None has been specified, handled by the @handle_error as a FetchJwtSvidError.

Fix :

Handling the NoneType before, by casting subject to a str only if it's not None.

        if subject != None:
            subject = str(subject)

[maxlambrecht]

Thanks for this PR, @telliere!

Would you rebase your branch?

[telliere]

Done,

Actually I have to say that the other PR opened would help me a lot, but I didn't have a look at the code

[telliere]

Was of the subject, sorry about that. Thanks for the review / The suggestions

[maxlambrecht]

Thanks, @telliere!