Add a jwt command to decode an access token locally

README.md

@@ -107,6 +107,9 @@ azd rest graph "Resources | summarize count() by type"
 # Show the signed-in Azure identity (tenant, app, scopes, expiry)
 azd rest whoami
 
+# Decode a token you already have and print its claims
+azd rest jwt "$(az account get-access-token --query accessToken -o tsv)"
+
 # Public API (no auth)
 azd rest get https://api.github.com/repos/Azure/azure-dev --no-auth
 

cli/src/internal/cmd/jwt.go

@@ -0,0 +1,52 @@
+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+// NewJWTCommand returns the jwt subcommand, which decodes an access token and
+// prints its claims locally without verifying the signature or making any
+// network call.
+func NewJWTCommand() *cobra.Command {
+	return &cobra.Command{
+		Use:   "jwt <token>",
+		Short: "Decode a JWT access token and show its claims",
+		Long: `Decode a JWT access token locally and print its claims.
+
+jwt reads the token from its argument, base64-decodes the claims segment, and
+prints the tenant, object ID, app ID, audience, username, granted scopes, roles,
+and expiry. With --format json it prints the full set of decoded claims.
+
+The signature is not verified and no network request is made. The raw token is
+never written to output. This is useful for inspecting a token from
+'az account get-access-token', an Authorization header, or a teammate.`,
+		Args: cobra.ExactArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return runJWT(args[0], outputFormat, cmd.OutOrStdout())
+		},
+	}
+}
+
+// runJWT decodes the token's claims and writes them to out. It is separated
+// from the cobra command so tests can exercise it directly.
+func runJWT(token, format string, out io.Writer) error {
+	claims, err := decodeJWTClaims(token)
+	if err != nil {
+		return fmt.Errorf("failed to decode token: %w", err)
+	}
+
+	if strings.EqualFold(format, "json") {
+		enc := json.NewEncoder(out)
+		enc.SetIndent("", "  ")
+		enc.SetEscapeHTML(false)
+		return enc.Encode(claims)
+	}
+
+	writeIdentityText(out, claimsToIdentity(claims))
+	return nil
+}

cli/src/internal/cmd/jwt_test.go

@@ -0,0 +1,81 @@
+package cmd
+
+import (
+	"bytes"
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+func TestRunJWT_Text(t *testing.T) {
+	token := makeJWT(t, map[string]any{
+		"tid":   "tenant-abc",
+		"oid":   "object-xyz",
+		"appid": "app-def",
+		"aud":   "https://management.azure.com",
+	})
+	var buf bytes.Buffer
+	if err := runJWT(token, "", &buf); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	out := buf.String()
+	for _, want := range []string{"Tenant:", "tenant-abc", "Object ID:", "object-xyz", "App ID:", "app-def"} {
+		if !strings.Contains(out, want) {
+			t.Fatalf("output missing %q:\n%s", want, out)
+		}
+	}
+	if strings.Contains(out, token) {
+		t.Fatalf("raw token must never be printed")
+	}
+}
+
+func TestRunJWT_JSONClaims(t *testing.T) {
+	token := makeJWT(t, map[string]any{
+		"tid": "tenant-abc",
+		"oid": "object-xyz",
+		"scp": "user_impersonation",
+	})
+	var buf bytes.Buffer
+	if err := runJWT(token, "json", &buf); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	var got map[string]any
+	if err := json.Unmarshal(buf.Bytes(), &got); err != nil {
+		t.Fatalf("output is not valid JSON: %v\n%s", err, buf.String())
+	}
+	if got["tid"] != "tenant-abc" || got["oid"] != "object-xyz" || got["scp"] != "user_impersonation" {
+		t.Fatalf("unexpected decoded claims: %#v", got)
+	}
+	if strings.Contains(buf.String(), token) {
+		t.Fatalf("raw token must never be printed")
+	}
+}
+
+func TestRunJWT_MalformedToken(t *testing.T) {
+	cases := map[string]string{
+		"empty":       "",
+		"two-segment": "header.payload",
+		"bad-base64":  "header.@@@@.sig",
+	}
+	for name, token := range cases {
+		t.Run(name, func(t *testing.T) {
+			var buf bytes.Buffer
+			if err := runJWT(token, "", &buf); err == nil {
+				t.Fatalf("expected error for %q", name)
+			}
+		})
+	}
+}
+
+func TestNewJWTCommand_RequiresToken(t *testing.T) {
+	cmd := NewJWTCommand()
+	if cmd.Use != "jwt <token>" {
+		t.Fatalf("unexpected Use: %q", cmd.Use)
+	}
+	if err := cmd.Args(cmd, nil); err == nil {
+		t.Fatal("expected error when no token argument is given")
+	}
+	if err := cmd.Args(cmd, []string{"a", "b"}); err == nil {
+		t.Fatal("expected error when more than one argument is given")
+	}
+}

cli/src/internal/cmd/root.go

@@ -253,6 +253,7 @@ Examples:
 		NewDoctorCommand(),
 		NewGraphCommand(),
 		NewWhoamiCommand(),
+		NewJWTCommand(),
 	)
 
 	return rootCmd

web/src/pages/reference.astro

@@ -39,6 +39,7 @@ const base = import.meta.env.BASE_URL;
               <tr><td><code>azd rest doctor</code></td><td>Diagnose authentication and scope detection issues</td></tr>
               <tr><td><code>azd rest graph &lt;kql-query&gt;</code></td><td>Run an Azure Resource Graph (KQL) query</td></tr>
               <tr><td><code>azd rest whoami</code></td><td>Show the authenticated Azure identity</td></tr>
+              <tr><td><code>azd rest jwt &lt;token&gt;</code></td><td>Decode a JWT access token and show its claims</td></tr>
               <tr><td><code>azd rest scope &lt;url&gt;</code></td><td>Preview the detected OAuth scope and auth mode for a URL</td></tr>
               <tr><td><code>azd rest version</code></td><td>Display extension version</td></tr>
             </tbody>