Define constants for all custom credentials

So far this is only `docker.context`.

Signed-off-by: Ian Campbell <ijc@docker.com>

Author: Ian Campbell

internal/commands/cnab.go

@@ -63,10 +63,10 @@ func prepareCredentialSet(contextName string, contextStore store.Store, b *bundl
 		if err != nil {
 			return nil, err
 		}
-		creds["docker.context"] = string(data)
+		creds[internal.CredentialDockerContextName] = string(data)
 	}
-	_, requiresDockerContext := b.Credentials["docker.context"]
-	_, hasDockerContext := creds["docker.context"]
+	_, requiresDockerContext := b.Credentials[internal.CredentialDockerContextName]
+	_, hasDockerContext := creds[internal.CredentialDockerContextName]
 	if requiresDockerContext && !hasDockerContext {
 		return nil, errors.New("no target context specified. Use --target-context= or DOCKER_TARGET_CONTEXT= to define it")
 	}

internal/names.go

@@ -32,6 +32,9 @@ const (
 	// ActionRenderName is the name of the custom "render" action
 	ActionRenderName = Namespace + "render"
 
+	// CredentialDockerContextName is the name of the credential containing a Docker context
+	CredentialDockerContextName = "docker.context"
+
 	// DockerStackOrchestratorEnvVar is the environment variable set by the CNAB runtime to select
 	// the stack orchestrator.
 	DockerStackOrchestratorEnvVar = "DOCKER_STACK_ORCHESTRATOR"

internal/packager/cnab.go

@@ -91,7 +91,7 @@ func ToCNAB(app *types.App, invocationImageName string) (*bundle.Bundle, error)
 
 	return &bundle.Bundle{
 		Credentials: map[string]bundle.Location{
-			"docker.context": {
+			internal.CredentialDockerContextName: {
 				Path: "/cnab/app/context.dockercontext",
 			},
 		},