all: Application Default Creds not included in context or tracing

[tam7t]

Is your feature request related to a problem? Please describe.

When ADC is used with instance-metadata

• resulting requests to instance metadata will not have RPC deadlines
• open-telemetry tracing of RPC calls wont include spans for retrieving metadata auth tokens (at least when using go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc)

This is due to:

• TokenSource.Token method should take in a Context golang/oauth2#262
• compute/metadata: accept request context #4483

Describe the solution you'd like

• I'd expect request deadlines to propagate to all downstream RPCs from the initial method call
• A way to enable tracing that separates out time spent talking to metadata server from time spent talking to the API

Describe alternatives you've considered

Additional context

[codyoss]

Hey @tam7t thanks for the request. I am not familiar with otelgrpc but I believe any requests that are made for ADC will all be HTTP based. To see this supported I agree that golang/oauth2#262 would need to be implemented first. Although that is an interface so we can't make changes to it, a new interface would need to be created and a migration path figured out for the many libraries using TokenSource today.

I don't think this request is really related to #4483 as that package just makes HTTP requests to a known endpoint, there is no auth involved.

This is something that is probably worth exploring and talking through but I think the changes would need to start in golang/oauth2 and then propagate to other packages. Would you mind opening this issue over on the oauth2 repo or adding some more context to golang/oauth2#262 why that change is important.

cc @broady

[tam7t]

Yeah, I only tagged #4483 because the oauth2 package depends on it in order to fetch the auth token from instance metadata. I will comment on the golang/oauth2 package with context.

[codyoss]

With our new auth module starting to roll out token calls will now accept a context from the call they originate from. Also the compute/metadata package was likewise recently updated.