feat(helm): prompt for password with helm repo add

Previously in Helm 2, 'helm repo add' would prompt for your password if
you only provided the --username flag. This helps prevent someone's
credentials from being logged in their shell's history, from showing
up in process lists, and from being seen by others nearby.

Closes #7174

Signed-off-by: Jack Weldon <jack.weldon.scm@gmail.com>

cmd/helm/repo_add.go

@@ -24,11 +24,13 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/gofrs/flock"
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
+	"golang.org/x/crypto/ssh/terminal"
 	"sigs.k8s.io/yaml"
 
 	"helm.sh/helm/v3/cmd/helm/require"
@@ -114,6 +116,16 @@ func (o *repoAddOptions) run(out io.Writer) error {
 		return errors.Errorf("repository name (%s) already exists, please specify a different name", o.name)
 	}
 
+	if o.username != "" && o.password == "" {
+		fmt.Fprint(out, "Password:")
+		password, err := terminal.ReadPassword(syscall.Stdin)
+		fmt.Fprintln(out)
+		if err != nil {
+			return err
+		}
+		o.password = string(password)
+	}
+
 	c := repo.Entry{
 		Name:                  o.name,
 		URL:                   o.url,