Support for kubeconfig files (#2053)

* Add support for authentication with kubeconfig files

* Update k8s plugin documentation

* Fix whitespace in README and tests

* Use clientcmd package to load kubeconfig file

plugin/kubernetes/setup.go

@@ -19,6 +19,7 @@ import (
 	"github.com/mholt/caddy"
 	"github.com/miekg/dns"
 	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/tools/clientcmd"
 )
 
 var log = clog.NewWithPlugin("kubernetes")
@@ -261,6 +262,17 @@ func ParseStanza(c *caddy.Controller) (*Kubernetes, error) {
 					return nil, fmt.Errorf("unable to parse ignore value: '%v'", ignore)
 				}
 			}
+		case "kubeconfig":
+			args := c.RemainingArgs()
+			if len(args) == 2 {
+				config := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
+					&clientcmd.ClientConfigLoadingRules{ExplicitPath: args[0]},
+					&clientcmd.ConfigOverrides{CurrentContext: args[1]},
+				)
+				k8s.ClientConfig = config
+				continue
+			}
+			return nil, c.ArgErr()
 		default:
 			return nil, c.Errf("unknown property '%s'", c.Val())
 		}