IdTokenCredentials fails to fetch license id claim when requested

[sjvanrossum]

Steps to reproduce

1. Create ComputeEngineCredentials on a GCE VM.
2. Derive IdTokenCredentials from the above with #setOptions() containing IdTokenProvider.Option.LICENSES_TRUE and optionally the implied IdTokenProvider.Option.FORMAT_FULL.
3. Observe lack of license id claims in payload.

Code example

new String(Base64.getUrlDecoder()
        .decode(IdTokenCredentials.newBuilder()
            .setIdTokenProvider(ComputeEngineCredentials.create())
            .setTargetAudience("https://foo.bar")
            .setOptions(Arrays.asList(
                IdTokenProvider.Option.FORMAT_FULL,
                IdTokenProvider.Option.LICENSES_TRUE))
            .build()
            .refreshAccessToken()
            .getTokenValue()
            .split("\\.")[1]),
    StandardCharsets.UTF_8)