Support env vars for registry auth when executing kp import

[tylerphelan]

When authenticating against registries during kp import:

• Allow for the use of credential-holding environment variables
• Allow for the use of multiple registries in the style of imgpkg (note: glob wildcards will not be supported)
  • Example of a single registry:

    REGISTRY=index.docker.io/grossum
    REGISTRY_USER=benevolentd
    REGISTRY_PASSWORD=g3nerator$Rule!
    

  • Example of multiple registries:

    REGISTRY_0=foo.dockerrepo.info/jmccarthy/lambda
    REGISTRY_USER_0=jmccarthy
    REGISTRY_PASSWORD_0=lambda4L1f3
    
    REGISTRY_1=bar.dockerrepo.info/rhickey/clojure
    REGISTRY_USER_1=rhickey
    REGISTRY_PASSWORD_1=JVM1sB3tt3r
    

[tomkennedy513]

Thinking out loud here, but shouldn't this extend to any place we use a keychain to interact with the registry in kp? I think it might be confusing if we only support these envs in one of the commands that reach out to to the registry

[ncarlson]

Thinking out loud here, but shouldn't this extend to any place we use a keychain to interact with the registry in kp? I think it might be confusing if we only support these envs in one of the commands that reach out to to the registry

Great idea.

I think we could do this anywhere authn.DefaultKeychain is used. We can replace keychain = authn.DefaultKeychain with a shortened version of this:

keychain := authn.NewMultiKeychain(
    authn.NewKeychainFromHelper(
	importpkg.NewCredHelperFromEnvVars(envVarRegistryUrl, envVarRegistryUser, envVarRegistryPassword)),
    defaultKeychain,
)

// maybe just:
//
// keychain := secret.NewDefaultEnvVarKeychain()
//
// which would also move the CredHelper out of helpers.go and into kpack-cli/pkg/secret/helpers.go (or credhelper.go)

The following files would be affected:

image/update_factory.go
image/factory.go
commands/lifecycle/patch.go
commands/import/import.go
commands/clusterstore/create.go
commands/clusterstore/add.go
commands/clusterstack/save.go
commands/clusterstack/patch.go
commands/clusterstack/create.go

[ncarlson]

perhaps pkg/dockercreds/ is a better location for this helper.