Add crane's auth command to facilitate logging into a registry (ko-bu…

…ild#243)

* Add crane's auth command to facilitate logging into a registry

* Add documentation about `ko auth login`

README.md

@@ -19,6 +19,17 @@
 GO111MODULE=on go get github.com/google/ko/cmd/ko
 ```
 
+## Authenticating
+
+The `ko` CLI makes extensive use of the container registry as a ubiquitous and
+standard object store. However, the typical model for authenticating with a
+container registry is via `docker login`, and `ko` does not require users to
+install `docker` locally. To facilitate logging in without `ko` we expose:
+
+```shell
+ko auth login my.registry.io -u username --password-stdin
+```
+
 ## The `ko` Model
 
 `ko` is built around a very simple extension to Go's model for expressing

cmd/ko/main.go

@@ -21,6 +21,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/logs"
 	"github.com/google/ko/pkg/commands"
 
+	cranecmd "github.com/google/go-containerregistry/cmd/crane/cmd"
 	"github.com/spf13/cobra"
 )
 
@@ -38,6 +39,10 @@ func main() {
 	}
 	commands.AddKubeCommands(cmds)
 
+	// Also add the auth group from crane to facilitate logging into a
+	// registry.
+	cmds.AddCommand(cranecmd.NewCmdAuth())
+
 	if err := cmds.Execute(); err != nil {
 		log.Fatalf("error during command execution: %v", err)
 	}