control, ipn, tailcfg: remove golang.org/x/oauth2 dep, add tailcfg.Oauth2Token

golang.org/x/oauth2 pulls in App Engine and grpc module dependencies,
screwing up builds that depend on this module.

Some background on the problem:
https://go.googlesource.com/proposal/+/master/design/36460-lazy-module-loading.md

Fixes tailscale/corp#1471

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/backend.go

@@ -8,7 +8,6 @@ import (
 	"net/http"
 	"time"
 
-	"golang.org/x/oauth2"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/empty"
@@ -28,7 +27,7 @@ const (
 	Running
 )
 
-// GoogleIDToken Type is the oauth2.Token.TokenType for the Google
+// GoogleIDToken Type is the tailcfg.Oauth2Token.TokenType for the Google
 // ID tokens used by the Android client.
 const GoogleIDTokenType = "ts_android_google_login"
 
@@ -142,7 +141,7 @@ type Backend interface {
 	// eventually.
 	StartLoginInteractive()
 	// Login logs in with an OAuth2 token.
-	Login(token *oauth2.Token)
+	Login(token *tailcfg.Oauth2Token)
 	// Logout terminates the current login session and stops the
 	// wireguard engine.
 	Logout()

ipn/fake_test.go

@@ -8,8 +8,8 @@ import (
 	"log"
 	"time"
 
-	"golang.org/x/oauth2"
 	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/netmap"
 )
 
@@ -46,7 +46,7 @@ func (b *FakeBackend) StartLoginInteractive() {
 	b.login()
 }
 
-func (b *FakeBackend) Login(token *oauth2.Token) {
+func (b *FakeBackend) Login(token *tailcfg.Oauth2Token) {
 	b.login()
 }
 

ipn/handle.go

@@ -8,8 +8,8 @@ import (
 	"sync"
 	"time"
 
-	"golang.org/x/oauth2"
 	"inet.af/netaddr"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/netmap"
 )
@@ -155,7 +155,7 @@ func (h *Handle) StartLoginInteractive() {
 	h.b.StartLoginInteractive()
 }
 
-func (h *Handle) Login(token *oauth2.Token) {
+func (h *Handle) Login(token *tailcfg.Oauth2Token) {
 	h.b.Login(token)
 }
 

ipn/ipnlocal/local.go

@@ -15,7 +15,6 @@ import (
 	"sync"
 	"time"
 
-	"golang.org/x/oauth2"
 	"inet.af/netaddr"
 	"tailscale.com/control/controlclient"
 	"tailscale.com/health"
@@ -1102,7 +1101,7 @@ func (b *LocalBackend) getEngineStatus() ipn.EngineStatus {
 }
 
 // Login implements Backend.
-func (b *LocalBackend) Login(token *oauth2.Token) {
+func (b *LocalBackend) Login(token *tailcfg.Oauth2Token) {
 	b.mu.Lock()
 	b.assertClientLocked()
 	c := b.c

ipn/message.go

@@ -15,7 +15,7 @@ import (
 	"log"
 	"time"
 
-	"golang.org/x/oauth2"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/structs"
 	"tailscale.com/version"
@@ -76,7 +76,7 @@ type Command struct {
 	Quit                  *NoArgs
 	Start                 *StartArgs
 	StartLoginInteractive *NoArgs
-	Login                 *oauth2.Token
+	Login                 *tailcfg.Oauth2Token
 	Logout                *NoArgs
 	SetPrefs              *SetPrefsArgs
 	SetWantRunning        *bool
@@ -296,7 +296,7 @@ func (bc *BackendClient) StartLoginInteractive() {
 	bc.send(Command{StartLoginInteractive: &NoArgs{}})
 }
 
-func (bc *BackendClient) Login(token *oauth2.Token) {
+func (bc *BackendClient) Login(token *tailcfg.Oauth2Token) {
 	bc.send(Command{Login: token})
 }
 

ipn/message_test.go

@@ -10,7 +10,7 @@ import (
 	"testing"
 	"time"
 
-	"golang.org/x/oauth2"
+	"tailscale.com/tailcfg"
 	"tailscale.com/tstest"
 )
 
@@ -176,7 +176,7 @@ func TestClientServer(t *testing.T) {
 	h.Logout()
 	flushUntil(NeedsLogin)
 
-	h.Login(&oauth2.Token{
+	h.Login(&tailcfg.Oauth2Token{
 		AccessToken: "google_id_token",
 		TokenType:   GoogleIDTokenType,
 	})