Add command to print JWT token for customer support

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

commands/print_token.go

@@ -0,0 +1,95 @@
+// Copyright (c) Alex Ellis 2017. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+package commands
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	faasCmd.AddCommand(printToken)
+}
+
+var printToken = &cobra.Command{
+	Use:   `print-token ./token.txt`,
+	Short: "Pretty-print the contents of a JWT token",
+	Example: `  # Print the contents of a JWT token
+  faas-cli print-token ./token.txt
+`,
+	RunE:   runPrintTokenE,
+	Hidden: true,
+}
+
+func runPrintTokenE(cmd *cobra.Command, args []string) error {
+
+	if len(args) < 1 {
+		return fmt.Errorf("provide the filename as an argument i.e. faas-cli print-token ./token.txt")
+	}
+
+	tokenFile := args[0]
+
+	data, err := os.ReadFile(tokenFile)
+	if err != nil {
+		return err
+	}
+
+	token := string(data)
+
+	jwtToken, err := unmarshalJwt(token)
+	if err != nil {
+		return err
+	}
+
+	j, err := json.MarshalIndent(jwtToken, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	fmt.Println(string(j))
+
+	return nil
+}
+
+type JwtToken struct {
+	Header  map[string]interface{} `json:"header"`
+	Payload map[string]interface{} `json:"payload"`
+}
+
+func unmarshalJwt(token string) (JwtToken, error) {
+
+	parts := strings.Split(token, ".")
+	if len(parts) != 3 {
+		return JwtToken{}, fmt.Errorf("token should have 3 parts, got %d", len(parts))
+	}
+
+	header, err := base64.RawURLEncoding.DecodeString(parts[0])
+	if err != nil {
+		return JwtToken{}, err
+	}
+
+	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
+	if err != nil {
+		return JwtToken{}, err
+	}
+
+	var jwt JwtToken
+
+	err = json.Unmarshal(header, &jwt.Header)
+	if err != nil {
+		return JwtToken{}, err
+	}
+
+	err = json.Unmarshal(payload, &jwt.Payload)
+	if err != nil {
+		return JwtToken{}, err
+	}
+
+	return jwt, nil
+}