Add 'kpod login' and 'kpod logout' commands

Signed-off-by: umohnani8 <umohnani@redhat.com>

cmd/kpod/logout.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/containers/image/pkg/docker/config"
+	"github.com/kubernetes-incubator/cri-o/libpod/common"
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+var (
+	logoutFlags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "authfile",
+			Usage: "Path of the authentication file. Default is ${XDG_RUNTIME_DIR}/containers/auth.json",
+		},
+		cli.BoolFlag{
+			Name:  "all, a",
+			Usage: "Remove the cached credentials for all registries in the auth file",
+		},
+	}
+	logoutDescription = "Remove the cached username and password for the registry."
+	logoutCommand     = cli.Command{
+		Name:        "logout",
+		Usage:       "logout of a container registry",
+		Description: logoutDescription,
+		Flags:       logoutFlags,
+		Action:      logoutCmd,
+		ArgsUsage:   "REGISTRY",
+	}
+)
+
+// logoutCmd uses the authentication package to remove the authenticated of a registry
+// stored in the auth.json file
+func logoutCmd(c *cli.Context) error {
+	args := c.Args()
+	if len(args) > 1 {
+		return errors.Errorf("too many arguments, logout takes only 1 argument")
+	}
+	var server string
+	if len(args) == 1 {
+		server = args[0]
+	}
+
+	sc := common.GetSystemContext("", c.String("authfile"))
+
+	if c.Bool("all") {
+		if err := config.RemoveAllAuthentication(sc); err != nil {
+			return err
+		}
+		fmt.Println("Remove login credentials for all registries")
+		return nil
+	}
+
+	err := config.RemoveAuthentication(sc, server)
+	switch err {
+	case nil:
+		fmt.Printf("Remove login credentials for %s\n", server)
+		return nil
+	case config.ErrNotLoggedIn:
+		return errors.Errorf("Not logged into %s\n", server)
+	default:
+		return errors.Wrapf(err, "error logging out of %q", server)
+	}
+}