quota_project_id is not used anywhere in google/

[zzctrlv]

The QuotaProjectID exists in config structs but is not read anywhere:
Is it meant to be attached when calling token_url for external accounts?

[zzctrlv]

I see. It is only used for gcloud CLI (https://google.aip.dev/auth/4113) and it will be up to the client library that integrates with ADC to choose to use this field or not.