migrate gplus to google oauth2 provider (#7885)

* migrate gplus to google oauth2 provider. this still provides support for old gplus connections.

* Update models/oauth2.go

Co-Authored-By: Antoine GIRARD <sapk@users.noreply.github.com>

* make vendor

vendor/google.golang.org/appengine/appengine.go

@@ -0,0 +1,135 @@
+// Copyright 2011 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+// Package appengine provides basic functionality for Google App Engine.
+//
+// For more information on how to write Go apps for Google App Engine, see:
+// https://cloud.google.com/appengine/docs/go/
+package appengine // import "google.golang.org/appengine"
+
+import (
+	"net/http"
+
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/context"
+
+	"google.golang.org/appengine/internal"
+)
+
+// The gophers party all night; the rabbits provide the beats.
+
+// Main is the principal entry point for an app running in App Engine.
+//
+// On App Engine Flexible it installs a trivial health checker if one isn't
+// already registered, and starts listening on port 8080 (overridden by the
+// $PORT environment variable).
+//
+// See https://cloud.google.com/appengine/docs/flexible/custom-runtimes#health_check_requests
+// for details on how to do your own health checking.
+//
+// On App Engine Standard it ensures the server has started and is prepared to
+// receive requests.
+//
+// Main never returns.
+//
+// Main is designed so that the app's main package looks like this:
+//
+//      package main
+//
+//      import (
+//              "google.golang.org/appengine"
+//
+//              _ "myapp/package0"
+//              _ "myapp/package1"
+//      )
+//
+//      func main() {
+//              appengine.Main()
+//      }
+//
+// The "myapp/packageX" packages are expected to register HTTP handlers
+// in their init functions.
+func Main() {
+	internal.Main()
+}
+
+// IsDevAppServer reports whether the App Engine app is running in the
+// development App Server.
+func IsDevAppServer() bool {
+	return internal.IsDevAppServer()
+}
+
+// IsStandard reports whether the App Engine app is running in the standard
+// environment. This includes both the first generation runtimes (<= Go 1.9)
+// and the second generation runtimes (>= Go 1.11).
+func IsStandard() bool {
+	return internal.IsStandard()
+}
+
+// IsFlex reports whether the App Engine app is running in the flexible environment.
+func IsFlex() bool {
+	return internal.IsFlex()
+}
+
+// IsAppEngine reports whether the App Engine app is running on App Engine, in either
+// the standard or flexible environment.
+func IsAppEngine() bool {
+	return internal.IsAppEngine()
+}
+
+// IsSecondGen reports whether the App Engine app is running on the second generation
+// runtimes (>= Go 1.11).
+func IsSecondGen() bool {
+	return internal.IsSecondGen()
+}
+
+// NewContext returns a context for an in-flight HTTP request.
+// This function is cheap.
+func NewContext(req *http.Request) context.Context {
+	return internal.ReqContext(req)
+}
+
+// WithContext returns a copy of the parent context
+// and associates it with an in-flight HTTP request.
+// This function is cheap.
+func WithContext(parent context.Context, req *http.Request) context.Context {
+	return internal.WithContext(parent, req)
+}
+
+// BlobKey is a key for a blobstore blob.
+//
+// Conceptually, this type belongs in the blobstore package, but it lives in
+// the appengine package to avoid a circular dependency: blobstore depends on
+// datastore, and datastore needs to refer to the BlobKey type.
+type BlobKey string
+
+// GeoPoint represents a location as latitude/longitude in degrees.
+type GeoPoint struct {
+	Lat, Lng float64
+}
+
+// Valid returns whether a GeoPoint is within [-90, 90] latitude and [-180, 180] longitude.
+func (g GeoPoint) Valid() bool {
+	return -90 <= g.Lat && g.Lat <= 90 && -180 <= g.Lng && g.Lng <= 180
+}
+
+// APICallFunc defines a function type for handling an API call.
+// See WithCallOverride.
+type APICallFunc func(ctx context.Context, service, method string, in, out proto.Message) error
+
+// WithAPICallFunc returns a copy of the parent context
+// that will cause API calls to invoke f instead of their normal operation.
+//
+// This is intended for advanced users only.
+func WithAPICallFunc(ctx context.Context, f APICallFunc) context.Context {
+	return internal.WithCallOverride(ctx, internal.CallOverrideFunc(f))
+}
+
+// APICall performs an API call.
+//
+// This is not intended for general use; it is exported for use in conjunction
+// with WithAPICallFunc.
+func APICall(ctx context.Context, service, method string, in, out proto.Message) error {
+	return internal.Call(ctx, service, method, in, out)
+}