exec credential provider: add install hint

This commit adds the ability for users to specify an install hint for
their exec credential provider binary.

In the exec credential provider workflow, if the exec credential binary
does not exist, then the user will see some sort of ugly

  exec: exec: "does-not-exist": executable file not found in $PATH

error message.  If some user downloads a kubeconfig from somewhere, they
may not know that kubectl is trying to use a binary to obtain
credentials to auth to the API, and scratch their head when they see
this error message.  Furthermore, even if a user does know that their
kubeconfig is trying to run a binary, they might not know how to obtain
the binary.  This install hint seeks to ease the above 2 user pains.

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

Kubernetes-commit: 94e2065df2eef3b198942efb156ef6e27abcc6f9

tools/clientcmd/client_config_test.go

@@ -624,6 +624,26 @@ func TestCreateMissingContext(t *testing.T) {
 	}
 }
 
+func TestCreateAuthConfigExecInstallHintCleanup(t *testing.T) {
+	config := createValidTestConfig()
+	clientBuilder := NewNonInteractiveClientConfig(*config, "clean", &ConfigOverrides{
+		AuthInfo: clientcmdapi.AuthInfo{
+			Exec: &clientcmdapi.ExecConfig{
+				APIVersion:  "client.authentication.k8s.io/v1alpha1",
+				Command:     "some-command",
+				InstallHint: "some install hint with \x1b[1mcontrol chars\x1b[0m\nand a newline",
+			},
+		},
+	}, nil)
+	cleanedInstallHint := "some install hint with U+001B[1mcontrol charsU+001B[0m\nand a newline"
+
+	clientConfig, err := clientBuilder.ClientConfig()
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	matchStringArg(cleanedInstallHint, clientConfig.ExecProvider.InstallHint, t)
+}
+
 func TestInClusterClientConfigPrecedence(t *testing.T) {
 	tt := []struct {
 		overrides *ConfigOverrides
@@ -850,3 +870,70 @@ users:
 	}
 
 }
+
+func TestCleanANSIEscapeCodes(t *testing.T) {
+	tests := []struct {
+		name    string
+		in, out string
+	}{
+		{
+			name: "DenyBoldCharacters",
+			in:   "\x1b[1mbold tuna\x1b[0m, fish, \x1b[1mbold marlin\x1b[0m",
+			out:  "U+001B[1mbold tunaU+001B[0m, fish, U+001B[1mbold marlinU+001B[0m",
+		},
+		{
+			name: "DenyCursorNavigation",
+			in:   "\x1b[2Aup up, \x1b[2Cright right",
+			out:  "U+001B[2Aup up, U+001B[2Cright right",
+		},
+		{
+			name: "DenyClearScreen",
+			in:   "clear: \x1b[2J",
+			out:  "clear: U+001B[2J",
+		},
+		{
+			name: "AllowSpaceCharactersUnchanged",
+			in:   "tuna\nfish\r\nmarlin\t\r\ntuna\vfish\fmarlin",
+		},
+		{
+			name: "AllowLetters",
+			in:   "alpha: \u03b1, beta: \u03b2, gamma: \u03b3",
+		},
+		{
+			name: "AllowMarks",
+			in: "tu\u0301na with a mark over the u, fi\u0302sh with a mark over the i," +
+				" ma\u030Arlin with a mark over the a",
+		},
+		{
+			name: "AllowNumbers",
+			in:   "t1na, f2sh, m3rlin, t12a, f34h, m56lin, t123, f456, m567n",
+		},
+		{
+			name: "AllowPunctuation",
+			in:   "\"here's a sentence; with! some...punctuation ;)\"",
+		},
+		{
+			name: "AllowSymbols",
+			in: "the integral of f(x) from 0 to n approximately equals the sum of f(x)" +
+				" from a = 0 to n, where a and n are natural numbers:" +
+				"\u222b\u2081\u207F f(x) dx \u2248 \u2211\u2090\u208C\u2081\u207F f(x)," +
+				" a \u2208 \u2115, n \u2208 \u2115",
+		},
+		{
+			name: "AllowSepatators",
+			in: "here is a paragraph separator\u2029and here\u2003are\u2003some" +
+				"\u2003em\u2003spaces",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if len(test.out) == 0 {
+				test.out = test.in
+			}
+
+			if actualOut := cleanANSIEscapeCodes(test.in); test.out != actualOut {
+				t.Errorf("expected %q, actual %q", test.out, actualOut)
+			}
+		})
+	}
+}