diff --git a/vendor/golang.org/x/oauth2/internal/token.go b/vendor/golang.org/x/oauth2/internal/token.go
new file mode 100644
index 0000000..a831b77
--- /dev/null
+++ b/vendor/golang.org/x/oauth2/internal/token.go
@@ -0,0 +1,277 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package internal
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"mime"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/net/context/ctxhttp"
+)
+
+// Token represents the credentials used to authorize
+// the requests to access protected resources on the OAuth 2.0
+// provider's backend.
+//
+// This type is a mirror of oauth2.Token and exists to break
+// an otherwise-circular dependency. Other internal packages
+// should convert this Token into an oauth2.Token before use.
+type Token struct {
+	// AccessToken is the token that authorizes and authenticates
+	// the requests.
+	AccessToken string
+
+	// TokenType is the type of token.
+	// The Type method returns either this or "Bearer", the default.
+	TokenType string
+
+	// RefreshToken is a token that's used by the application
+	// (as opposed to the user) to refresh the access token
+	// if it expires.
+	RefreshToken string
+
+	// Expiry is the optional expiration time of the access token.
+	//
+	// If zero, TokenSource implementations will reuse the same
+	// token forever and RefreshToken or equivalent
+	// mechanisms for that TokenSource will not be used.
+	Expiry time.Time
+
+	// Raw optionally contains extra metadata from the server
+	// when updating a token.
+	Raw interface{}
+}
+
+// tokenJSON is the struct representing the HTTP response from OAuth2
+// providers returning a token in JSON form.
+type tokenJSON struct {
+	AccessToken  string         `json:"access_token"`
+	TokenType    string         `json:"token_type"`
+	RefreshToken string         `json:"refresh_token"`
+	ExpiresIn    expirationTime `json:"expires_in"` // at least PayPal returns string, while most return number
+	Expires      expirationTime `json:"expires"`    // broken Facebook spelling of expires_in
+}
+
+func (e *tokenJSON) expiry() (t time.Time) {
+	if v := e.ExpiresIn; v != 0 {
+		return time.Now().Add(time.Duration(v) * time.Second)
+	}
+	if v := e.Expires; v != 0 {
+		return time.Now().Add(time.Duration(v) * time.Second)
+	}
+	return
+}
+
+type expirationTime int32
+
+func (e *expirationTime) UnmarshalJSON(b []byte) error {
+	var n json.Number
+	err := json.Unmarshal(b, &n)
+	if err != nil {
+		return err
+	}
+	i, err := n.Int64()
+	if err != nil {
+		return err
+	}
+	*e = expirationTime(i)
+	return nil
+}
+
+var brokenAuthHeaderProviders = []string{
+	"https://accounts.google.com/",
+	"https://api.codeswholesale.com/oauth/token",
+	"https://api.dropbox.com/",
+	"https://api.dropboxapi.com/",
+	"https://api.instagram.com/",
+	"https://api.netatmo.net/",
+	"https://api.odnoklassniki.ru/",
+	"https://api.pushbullet.com/",
+	"https://api.soundcloud.com/",
+	"https://api.twitch.tv/",
+	"https://id.twitch.tv/",
+	"https://app.box.com/",
+	"https://api.box.com/",
+	"https://connect.stripe.com/",
+	"https://login.mailchimp.com/",
+	"https://login.microsoftonline.com/",
+	"https://login.salesforce.com/",
+	"https://login.windows.net",
+	"https://login.live.com/",
+	"https://login.live-int.com/",
+	"https://oauth.sandbox.trainingpeaks.com/",
+	"https://oauth.trainingpeaks.com/",
+	"https://oauth.vk.com/",
+	"https://openapi.baidu.com/",
+	"https://slack.com/",
+	"https://test-sandbox.auth.corp.google.com",
+	"https://test.salesforce.com/",
+	"https://user.gini.net/",
+	"https://www.douban.com/",
+	"https://www.googleapis.com/",
+	"https://www.linkedin.com/",
+	"https://www.strava.com/oauth/",
+	"https://www.wunderlist.com/oauth/",
+	"https://api.patreon.com/",
+	"https://sandbox.codeswholesale.com/oauth/token",
+	"https://api.sipgate.com/v1/authorization/oauth",
+	"https://api.medium.com/v1/tokens",
+	"https://log.finalsurge.com/oauth/token",
+	"https://multisport.todaysplan.com.au/rest/oauth/access_token",
+	"https://whats.todaysplan.com.au/rest/oauth/access_token",
+	"https://stackoverflow.com/oauth/access_token",
+	"https://account.health.nokia.com",
+	"https://accounts.zoho.com",
+	"https://gitter.im/login/oauth/token",
+	"https://openid-connect.onelogin.com/oidc",
+	"https://api.dailymotion.com/oauth/token",
+}
+
+// brokenAuthHeaderDomains lists broken providers that issue dynamic endpoints.
+var brokenAuthHeaderDomains = []string{
+	".auth0.com",
+	".force.com",
+	".myshopify.com",
+	".okta.com",
+	".oktapreview.com",
+}
+
+func RegisterBrokenAuthHeaderProvider(tokenURL string) {
+	brokenAuthHeaderProviders = append(brokenAuthHeaderProviders, tokenURL)
+}
+
+// providerAuthHeaderWorks reports whether the OAuth2 server identified by the tokenURL
+// implements the OAuth2 spec correctly
+// See https://code.google.com/p/goauth2/issues/detail?id=31 for background.
+// In summary:
+// - Reddit only accepts client secret in the Authorization header
+// - Dropbox accepts either it in URL param or Auth header, but not both.
+// - Google only accepts URL param (not spec compliant?), not Auth header
+// - Stripe only accepts client secret in Auth header with Bearer method, not Basic
+func providerAuthHeaderWorks(tokenURL string) bool {
+	for _, s := range brokenAuthHeaderProviders {
+		if strings.HasPrefix(tokenURL, s) {
+			// Some sites fail to implement the OAuth2 spec fully.
+			return false
+		}
+	}
+
+	if u, err := url.Parse(tokenURL); err == nil {
+		for _, s := range brokenAuthHeaderDomains {
+			if strings.HasSuffix(u.Host, s) {
+				return false
+			}
+		}
+	}
+
+	// Assume the provider implements the spec properly
+	// otherwise. We can add more exceptions as they're
+	// discovered. We will _not_ be adding configurable hooks
+	// to this package to let users select server bugs.
+	return true
+}
+
+func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string, v url.Values) (*Token, error) {
+	bustedAuth := !providerAuthHeaderWorks(tokenURL)
+	if bustedAuth {
+		if clientID != "" {
+			v.Set("client_id", clientID)
+		}
+		if clientSecret != "" {
+			v.Set("client_secret", clientSecret)
+		}
+	}
+	req, err := http.NewRequest("POST", tokenURL, strings.NewReader(v.Encode()))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	if !bustedAuth {
+		req.SetBasicAuth(url.QueryEscape(clientID), url.QueryEscape(clientSecret))
+	}
+	r, err := ctxhttp.Do(ctx, ContextClient(ctx), req)
+	if err != nil {
+		return nil, err
+	}
+	defer r.Body.Close()
+	body, err := ioutil.ReadAll(io.LimitReader(r.Body, 1<<20))
+	if err != nil {
+		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
+	}
+	if code := r.StatusCode; code < 200 || code > 299 {
+		return nil, &RetrieveError{
+			Response: r,
+			Body:     body,
+		}
+	}
+
+	var token *Token
+	content, _, _ := mime.ParseMediaType(r.Header.Get("Content-Type"))
+	switch content {
+	case "application/x-www-form-urlencoded", "text/plain":
+		vals, err := url.ParseQuery(string(body))
+		if err != nil {
+			return nil, err
+		}
+		token = &Token{
+			AccessToken:  vals.Get("access_token"),
+			TokenType:    vals.Get("token_type"),
+			RefreshToken: vals.Get("refresh_token"),
+			Raw:          vals,
+		}
+		e := vals.Get("expires_in")
+		if e == "" {
+			// TODO(jbd): Facebook's OAuth2 implementation is broken and
+			// returns expires_in field in expires. Remove the fallback to expires,
+			// when Facebook fixes their implementation.
+			e = vals.Get("expires")
+		}
+		expires, _ := strconv.Atoi(e)
+		if expires != 0 {
+			token.Expiry = time.Now().Add(time.Duration(expires) * time.Second)
+		}
+	default:
+		var tj tokenJSON
+		if err = json.Unmarshal(body, &tj); err != nil {
+			return nil, err
+		}
+		token = &Token{
+			AccessToken:  tj.AccessToken,
+			TokenType:    tj.TokenType,
+			RefreshToken: tj.RefreshToken,
+			Expiry:       tj.expiry(),
+			Raw:          make(map[string]interface{}),
+		}
+		json.Unmarshal(body, &token.Raw) // no error checks for optional fields
+	}
+	// Don't overwrite `RefreshToken` with an empty value
+	// if this was a token refreshing request.
+	if token.RefreshToken == "" {
+		token.RefreshToken = v.Get("refresh_token")
+	}
+	if token.AccessToken == "" {
+		return token, errors.New("oauth2: server response missing access_token")
+	}
+	return token, nil
+}
+
+type RetrieveError struct {
+	Response *http.Response
+	Body     []byte
+}
+
+func (r *RetrieveError) Error() string {
+	return fmt.Sprintf("oauth2: cannot fetch token: %v\nResponse: %s", r.Response.Status, r.Body)
+}