feat(auth): store and retrieve auth token from home directory by default (#2)

internal/command/api/flag/flag.go

@@ -2,7 +2,6 @@ package flag
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"strings"
 
@@ -12,6 +11,11 @@ import (
 	"github.com/urfave/cli/v2"
 )
 
+const (
+	AuthTokenDefaultHomePath  = "$HOME/.config/emissary/auth-token"
+	AuthTokenDefaultLocalPath = ".emissary-token"
+)
+
 func ComposeFlags(flags ...cli.Flag) []cli.Flag {
 	baseFlags := []cli.Flag{
 		&cli.StringFlag{
@@ -37,10 +41,10 @@ func ComposeFlags(flags ...cli.Flag) []cli.Flag {
 			Aliases: []string{"t"},
 			Usage:   "use `TOKEN` as authentication token",
 		},
-		&cli.StringFlag{
+		&cli.StringSliceFlag{
 			Name:      "token-file",
 			Usage:     "use `TOKEN_FILE` as file containing the authentication token",
-			Value:     ".emissary-token",
+			Value:     cli.NewStringSlice(AuthTokenDefaultLocalPath, AuthTokenDefaultHomePath),
 			TakesFile: true,
 		},
 	}
@@ -55,14 +59,14 @@ type BaseFlags struct {
 	Format     format.Format
 	OutputMode format.OutputMode
 	Token      string
-	TokenFile  string
+	TokenFiles []string
 }
 
 func GetBaseFlags(ctx *cli.Context) *BaseFlags {
 	serverURL := ctx.String("server")
 	rawFormat := ctx.String("format")
 	rawOutputMode := ctx.String("output-mode")
-	tokenFile := ctx.String("token-file")
+	tokenFiles := ctx.StringSlice("token-file")
 	token := ctx.String("token")
 
 	return &BaseFlags{
@@ -70,7 +74,7 @@ func GetBaseFlags(ctx *cli.Context) *BaseFlags {
 		Format:     format.Format(rawFormat),
 		OutputMode: format.OutputMode(rawOutputMode),
 		Token:      token,
-		TokenFile:  tokenFile,
+		TokenFiles: tokenFiles,
 	}
 }
 
@@ -79,18 +83,20 @@ func GetToken(flags *BaseFlags) (string, error) {
 		return flags.Token, nil
 	}
 
-	if flags.TokenFile == "" {
-		return "", nil
+	for _, tokenFile := range flags.TokenFiles {
+		tokenFile = os.ExpandEnv(tokenFile)
+
+		rawToken, err := os.ReadFile(tokenFile)
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
+			return "", errors.WithStack(err)
+		}
+
+		if rawToken == nil {
+			continue
+		}
+
+		return strings.TrimSpace(string(rawToken)), nil
 	}
 
-	rawToken, err := ioutil.ReadFile(flags.TokenFile)
-	if err != nil && !errors.Is(err, os.ErrNotExist) {
-		return "", errors.WithStack(err)
-	}
-
-	if rawToken == nil {
-		return "", nil
-	}
-
-	return strings.TrimSpace(string(rawToken)), nil
+	return "", nil
 }