Add --token-file support

pkg/cli/agent/agent.go

@@ -3,7 +3,10 @@ package agent
 import (
 	"context"
 	"fmt"
+	"io/ioutil"
 	"os"
+	"strings"
+	"time"
 
 	"github.com/rancher/k3s/pkg/agent"
 	"github.com/rancher/k3s/pkg/cli/cmds"
@@ -13,11 +16,37 @@ import (
 	"github.com/urfave/cli"
 )
 
+func readToken(path string) (string, error) {
+	if path == "" {
+		return "", nil
+	}
+
+	for {
+		tokenBytes, err := ioutil.ReadFile(path)
+		if err == nil {
+			return strings.TrimSpace(string(tokenBytes)), nil
+		} else if os.IsNotExist(err) {
+			logrus.Infof("Waiting for %s to be available\n", path)
+			time.Sleep(2 * time.Second)
+		} else {
+			return "", err
+		}
+	}
+}
+
 func Run(ctx *cli.Context) error {
 	if os.Getuid() != 0 {
 		return fmt.Errorf("agent must be ran as root")
 	}
 
+	if cmds.AgentConfig.TokenFile != "" {
+		token, err := readToken(cmds.AgentConfig.TokenFile)
+		if err != nil {
+			return err
+		}
+		cmds.AgentConfig.Token = token
+	}
+
 	if cmds.AgentConfig.Token == "" && cmds.AgentConfig.ClusterSecret == "" {
 		return fmt.Errorf("--token is required")
 	}

pkg/cli/cmds/agent.go

@@ -9,6 +9,7 @@ import (
 
 type Agent struct {
 	Token         string
+	TokenFile     string
 	ServerURL     string
 	DataDir       string
 	NodeIP        string
@@ -53,6 +54,12 @@ func NewAgentCommand(action func(ctx *cli.Context) error) cli.Command {
 				EnvVar:      "K3S_TOKEN",
 				Destination: &AgentConfig.Token,
 			},
+			cli.StringFlag{
+				Name:        "token-file",
+				Usage:       "Token file to use for authentication",
+				EnvVar:      "K3S_TOKEN_FILE",
+				Destination: &AgentConfig.TokenFile,
+			},
 			cli.StringFlag{
 				Name:        "server,s",
 				Usage:       "Server to connect to",