Update internal GCP Auth to use new SignJWT endpoint

[catsby]

Updates Waypoints' internal GCP auth to use GCP's IAM Service Account Credential endpoint for signing JWTs, as the IAM endpoint versions are deprecated and being turned off (not totally sure when but speculation/inference is around July 1, 2021). See https://cloud.google.com/iam/docs/migrating-to-credentials-api for more information on the deprecation and migration.

I'm honestly not sure where this is used and there isn't a directly related test file associated with this, so I have not tested other than to ensure the project still compiles.

See also for more backstory:

• GCP SignJwt deprecation vault-plugin-auth-gcp#100
• Add new ServiceAccountCredentialsTemplate, mark ServiceAccountTemplate as deprecated go-gcp-common#4
• Update gcp-common/IAM Credentials API usage vault-plugin-auth-gcp#108
• Update Agent Auth with GCP to use new SignJWT endpoint vault#11473

Note: I added the pr/no-changelog label because I didn't feel this change warranted it, but let me know if you'd prefer one added

[briancain]

Hey @catsby ! Thanks.

I think we'll also want to update 👇🏻 too?

waypoint/builtin/google/cloudrun/platform.go

Lines 154 to 157 in 1a46a87

	apiResource := fmt.Sprintf("projects/%s/serviceAccounts/%s",
	p.config.Project,
	p.config.ServiceAccountName,
	)

I could see this needing a CHANGELOG entry only because in the future, older Waypoints will probably fail once the endpoint is deprecated? It might be nice in that sense to remember when the update to the new endpoint usage was released.

[catsby]

Hey @briancain - I believe the usage in google/cloudrun/platform.go is correct; the URL change from projects/%s/serviceAccounts/%s to projects/-/serviceAccounts/%s only pertains to the Service Account Credentials API. The API to test permissions seems to be correct. The changes required only matter for signing JWTs, and I'm not finding spots in the Waypoint code where that method is otherwise called. Let me know what you think, maybe I'm missing something?

[krantzinator]

ran through a release to GCP with this and it works 🎉

[briancain]

👍🏻 looks good!