scout hint: tell user logging in is required

The `docker scout quickview` hint, displayed
after a user pulls or builds an image, only
works if the user is logged in to Hub.

Check if user isn't logged in, and make hint
more explicit in this case.

Signed-off-by: Laura Brehm <[email protected]>

cli/mobycli/scout_suggest.go

@@ -20,7 +20,9 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"time"
 
+	"github.com/docker/cli/cli/config"
 	"github.com/docker/compose/v2/pkg/utils"
 
 	"github.com/fatih/color"
@@ -53,10 +55,14 @@ func displayScoutQuickViewSuggestMsg(image string) {
 	}
 	out := os.Stderr
 	b := color.New(color.Bold)
-	_, _ = fmt.Fprintln(out)
-	_, _ = b.Fprintln(out, "What's Next?")
-	_, _ = fmt.Fprintf(out, "  View summary of image vulnerabilities and recommendations → %s", color.CyanString("docker scout quickview%s", image))
-	_, _ = fmt.Fprintln(out)
+
+	_, _ = b.Fprintln(out, "\nWhat's Next?")
+	if !hubLoggedIn() {
+		_, _ = fmt.Fprintf(out, "  View summary of image vulnerabilities and recommendations (login required) → %s\n", color.CyanString("docker scout quickview%s", image))
+		_, _ = fmt.Fprint(out, "  To sign in, use the `docker login` command or sign in via Docker Desktop\n")
+	} else {
+		_, _ = fmt.Fprintf(out, "  View summary of image vulnerabilities and recommendations → %s\n", color.CyanString("docker scout quickview%s", image))
+	}
 }
 
 func pulledImageFromArgs(args []string) string {
@@ -74,3 +80,25 @@ func pulledImageFromArgs(args []string) string {
 	}
 	return image
 }
+
+// hubLoggedIn checks whether the user has credentials configured
+// for Docker Hub. This can be an expensive operation, so use it
+// mindfully.
+func hubLoggedIn() bool {
+	result := make(chan bool)
+	go func() {
+		hubAuth, err := config.LoadDefaultConfigFile(nil).GetAuthConfig("index.docker.io")
+		if err != nil {
+			// preserve original behaviour if we fail to fetch creds
+			result <- true
+		}
+		result <- hubAuth.Username != ""
+	}()
+	select {
+	case loggedIn := <-result:
+		return loggedIn
+	case <-time.After(100 * time.Millisecond):
+		// preserve original behaviour if we time out
+		return true
+	}
+}