cli: Fix a bug where self token lookups via token CLI flag failed. (#26183)

The meta client looks for both an environment variable and a CLI
flag when generating a client. The CLI UUID checker needs to do
this also, so we account for users using both env vars and CLI
flag tokens.

.changelog/26183.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+cli: Fixed a bug where the `acl token self` command only performed lookups for tokens set as environment variables and not by the `-token` flag.
+```

command/acl_token_self.go

@@ -65,15 +65,26 @@ func (c *ACLTokenSelfCommand) Run(args []string) int {
 		return 1
 	}
 
-	// Check what kind of token we have available
-	envToken := os.Getenv("NOMAD_TOKEN")
-	if envToken == "" {
-		c.Ui.Error("No token present in the environment")
+	// To get the authentication token, we must perform the same steps as the
+	// command meta and API client perform. This is because the token may be set
+	// as an environment variable or as a CLI flag.
+	//
+	// The environment variable is grabbed first. If this is not set, the
+	// resulting string is empty.
+	authToken := os.Getenv("NOMAD_TOKEN")
+
+	// If the CLI flag is set, it will override the environment variable.
+	if c.token != "" {
+		authToken = c.token
+	}
+
+	if authToken == "" {
+		c.Ui.Error("No token present in the environment or set via the CLI flag")
 		return 1
 	}
 
 	// Does this look like a Nomad ACL token?
-	if helper.IsUUID(envToken) {
+	if helper.IsUUID(authToken) {
 		token, _, err := client.ACLTokens().Self(nil)
 		if err != nil {
 			c.Ui.Error(fmt.Sprintf("Error fetching self token: %s", err))

command/acl_token_self_test.go

@@ -53,3 +53,34 @@ func TestACLTokenSelfCommand_ViaEnvVar(t *testing.T) {
 	out := ui.OutputWriter.String()
 	must.StrContains(t, out, mockToken.AccessorID)
 }
+
+func TestACLTokenSelfCommand_ViaFlag(t *testing.T) {
+	config := func(c *agent.Config) {
+		c.ACL.Enabled = true
+	}
+
+	srv, _, url := testServer(t, true, config)
+	defer srv.Shutdown()
+
+	state := srv.Agent.Server().State()
+
+	// Bootstrap an initial ACL token
+	token := srv.RootToken
+	must.NotNil(t, token)
+
+	ui := cli.NewMockUi()
+	cmd := &ACLTokenSelfCommand{Meta: Meta{Ui: ui, flagAddress: url}}
+
+	// Create a valid token
+	mockToken := mock.ACLToken()
+	mockToken.Policies = []string{acl.PolicyWrite}
+	mockToken.SetHash()
+	must.NoError(t, state.UpsertACLTokens(structs.MsgTypeTestSetup, 1000, []*structs.ACLToken{mockToken}))
+
+	// Fetch info on a token with a valid token
+	code := cmd.Run([]string{"-address=" + url, "-token=" + mockToken.SecretID})
+	must.Zero(t, code)
+
+	// Check the output
+	must.StrContains(t, ui.OutputWriter.String(), mockToken.AccessorID)
+}