exec credential provider: InteractiveMode support

The value here is that the exec plugin author can use the kubeconfig to assert
how standard input is treated with respect to the exec plugin, e.g.,
- an exec plugin author can ensure that kubectl fails if it cannot provide
  standard input to an exec plugin that needs it (Always)
- an exec plugin author can ensure that an client-go process will still call an
  exec plugin that prefers standard input even if standard input is not
  available (IfAvailable)

Signed-off-by: Andrew Keesler <akeesler@vmware.com>

Kubernetes-commit: cd83d89ac94c5b61fdd38840098e7223e5af0d34

tools/clientcmd/api/v1/defaults_test.go

@@ -0,0 +1,84 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestSetDefaults_Config(t *testing.T) {
+	tests := []struct {
+		name        string
+		in, wantOut *ExecConfig
+	}{
+		{
+			name: "alpha exec API with empty interactive mode",
+			in:   &ExecConfig{APIVersion: "client.authentication.k8s.io/v1alpha1"},
+			wantOut: &ExecConfig{
+				APIVersion:      "client.authentication.k8s.io/v1alpha1",
+				InteractiveMode: IfAvailableExecInteractiveMode,
+			},
+		},
+		{
+			name: "beta exec API with empty interactive mode",
+			in:   &ExecConfig{APIVersion: "client.authentication.k8s.io/v1beta1"},
+			wantOut: &ExecConfig{
+				APIVersion:      "client.authentication.k8s.io/v1beta1",
+				InteractiveMode: IfAvailableExecInteractiveMode,
+			},
+		},
+		{
+			name: "alpha exec API with set interactive mode",
+			in: &ExecConfig{
+				APIVersion:      "client.authentication.k8s.io/v1alpha1",
+				InteractiveMode: NeverExecInteractiveMode,
+			},
+			wantOut: &ExecConfig{
+				APIVersion:      "client.authentication.k8s.io/v1alpha1",
+				InteractiveMode: NeverExecInteractiveMode,
+			},
+		},
+		{
+			name: "beta exec API with set interactive mode",
+			in: &ExecConfig{
+				APIVersion:      "client.authentication.k8s.io/v1beta1",
+				InteractiveMode: NeverExecInteractiveMode,
+			},
+			wantOut: &ExecConfig{
+				APIVersion:      "client.authentication.k8s.io/v1beta1",
+				InteractiveMode: NeverExecInteractiveMode,
+			},
+		},
+		{
+			name:    "v1 exec API with empty interactive mode",
+			in:      &ExecConfig{APIVersion: "client.authentication.k8s.io/v1"},
+			wantOut: &ExecConfig{APIVersion: "client.authentication.k8s.io/v1"},
+		},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			gotOut := test.in.DeepCopy()
+			SetDefaults_ExecConfig(gotOut)
+			if diff := cmp.Diff(test.wantOut, gotOut); diff != "" {
+				t.Errorf("unexpected defaulting; -want, +got:\n %s", diff)
+			}
+		})
+	}
+}