Remove x/net/context vendor by using std package (#5202)

* Update dep github.com/markbates/goth

* Update dep github.com/blevesearch/bleve

* Update dep golang.org/x/oauth2

* Fix github.com/blevesearch/bleve to c74e08f039e56cef576e4336382b2a2d12d9e026

* Update dep golang.org/x/oauth2

12 files changed, 388 insertions, 149 deletions

diff --git a/vendor/golang.org/x/net/context/ctxhttp/ctxhttp.go b/vendor/golang.org/x/net/context/ctxhttp/ctxhttp.go
new file mode 100644
index 0000000000..606cf1f972
--- /dev/null
+++ b/vendor/golang.org/x/net/context/ctxhttp/ctxhttp.go
@@ -0,0 +1,74 @@
+// Copyright 2016 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.
+
+// +build go1.7
+
+// Package ctxhttp provides helper functions for performing context-aware HTTP requests.
+package ctxhttp // import "golang.org/x/net/context/ctxhttp"
+
+import (
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"golang.org/x/net/context"
+)
+
+// Do sends an HTTP request with the provided http.Client and returns
+// an HTTP response.
+//
+// If the client is nil, http.DefaultClient is used.
+//
+// The provided ctx must be non-nil. If it is canceled or times out,
+// ctx.Err() will be returned.
+func Do(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
+	if client == nil {
+		client = http.DefaultClient
+	}
+	resp, err := client.Do(req.WithContext(ctx))
+	// If we got an error, and the context has been canceled,
+	// the context's error is probably more useful.
+	if err != nil {
+		select {
+		case <-ctx.Done():
+			err = ctx.Err()
+		default:
+		}
+	}
+	return resp, err
+}
+
+// Get issues a GET request via the Do function.
+func Get(ctx context.Context, client *http.Client, url string) (*http.Response, error) {
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	return Do(ctx, client, req)
+}
+
+// Head issues a HEAD request via the Do function.
+func Head(ctx context.Context, client *http.Client, url string) (*http.Response, error) {
+	req, err := http.NewRequest("HEAD", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	return Do(ctx, client, req)
+}
+
+// Post issues a POST request via the Do function.
+func Post(ctx context.Context, client *http.Client, url string, bodyType string, body io.Reader) (*http.Response, error) {
+	req, err := http.NewRequest("POST", url, body)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", bodyType)
+	return Do(ctx, client, req)
+}
+
+// PostForm issues a POST request via the Do function.
+func PostForm(ctx context.Context, client *http.Client, url string, data url.Values) (*http.Response, error) {
+	return Post(ctx, client, url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
+}
diff --git a/vendor/golang.org/x/net/context/ctxhttp/ctxhttp_pre17.go b/vendor/golang.org/x/net/context/ctxhttp/ctxhttp_pre17.go
new file mode 100644
index 0000000000..926870cc23
--- /dev/null
+++ b/vendor/golang.org/x/net/context/ctxhttp/ctxhttp_pre17.go
@@ -0,0 +1,147 @@
+// Copyright 2015 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.
+
+// +build !go1.7
+
+package ctxhttp // import "golang.org/x/net/context/ctxhttp"
+
+import (
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"golang.org/x/net/context"
+)
+
+func nop() {}
+
+var (
+	testHookContextDoneBeforeHeaders = nop
+	testHookDoReturned               = nop
+	testHookDidBodyClose             = nop
+)
+
+// Do sends an HTTP request with the provided http.Client and returns an HTTP response.
+// If the client is nil, http.DefaultClient is used.
+// If the context is canceled or times out, ctx.Err() will be returned.
+func Do(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
+	if client == nil {
+		client = http.DefaultClient
+	}
+
+	// TODO(djd): Respect any existing value of req.Cancel.
+	cancel := make(chan struct{})
+	req.Cancel = cancel
+
+	type responseAndError struct {
+		resp *http.Response
+		err  error
+	}
+	result := make(chan responseAndError, 1)
+
+	// Make local copies of test hooks closed over by goroutines below.
+	// Prevents data races in tests.
+	testHookDoReturned := testHookDoReturned
+	testHookDidBodyClose := testHookDidBodyClose
+
+	go func() {
+		resp, err := client.Do(req)
+		testHookDoReturned()
+		result <- responseAndError{resp, err}
+	}()
+
+	var resp *http.Response
+
+	select {
+	case <-ctx.Done():
+		testHookContextDoneBeforeHeaders()
+		close(cancel)
+		// Clean up after the goroutine calling client.Do:
+		go func() {
+			if r := <-result; r.resp != nil {
+				testHookDidBodyClose()
+				r.resp.Body.Close()
+			}
+		}()
+		return nil, ctx.Err()
+	case r := <-result:
+		var err error
+		resp, err = r.resp, r.err
+		if err != nil {
+			return resp, err
+		}
+	}
+
+	c := make(chan struct{})
+	go func() {
+		select {
+		case <-ctx.Done():
+			close(cancel)
+		case <-c:
+			// The response's Body is closed.
+		}
+	}()
+	resp.Body = &notifyingReader{resp.Body, c}
+
+	return resp, nil
+}
+
+// Get issues a GET request via the Do function.
+func Get(ctx context.Context, client *http.Client, url string) (*http.Response, error) {
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	return Do(ctx, client, req)
+}
+
+// Head issues a HEAD request via the Do function.
+func Head(ctx context.Context, client *http.Client, url string) (*http.Response, error) {
+	req, err := http.NewRequest("HEAD", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	return Do(ctx, client, req)
+}
+
+// Post issues a POST request via the Do function.
+func Post(ctx context.Context, client *http.Client, url string, bodyType string, body io.Reader) (*http.Response, error) {
+	req, err := http.NewRequest("POST", url, body)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", bodyType)
+	return Do(ctx, client, req)
+}
+
+// PostForm issues a POST request via the Do function.
+func PostForm(ctx context.Context, client *http.Client, url string, data url.Values) (*http.Response, error) {
+	return Post(ctx, client, url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
+}
+
+// notifyingReader is an io.ReadCloser that closes the notify channel after
+// Close is called or a Read fails on the underlying ReadCloser.
+type notifyingReader struct {
+	io.ReadCloser
+	notify chan<- struct{}
+}
+
+func (r *notifyingReader) Read(p []byte) (int, error) {
+	n, err := r.ReadCloser.Read(p)
+	if err != nil && r.notify != nil {
+		close(r.notify)
+		r.notify = nil
+	}
+	return n, err
+}
+
+func (r *notifyingReader) Close() error {
+	err := r.ReadCloser.Close()
+	if r.notify != nil {
+		close(r.notify)
+		r.notify = nil
+	}
+	return err
+}
diff --git a/vendor/golang.org/x/oauth2/LICENSE b/vendor/golang.org/x/oauth2/LICENSE
index d02f24fd52..6a66aea5ea 100644
--- a/vendor/golang.org/x/oauth2/LICENSE
+++ b/vendor/golang.org/x/oauth2/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2009 The oauth2 Authors. All rights reserved.
+Copyright (c) 2009 The Go Authors. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are
diff --git a/vendor/golang.org/x/oauth2/client_appengine.go b/vendor/golang.org/x/oauth2/client_appengine.go
deleted file mode 100644
index 8962c49d1d..0000000000
--- a/vendor/golang.org/x/oauth2/client_appengine.go
+++ /dev/null
@@ -1,25 +0,0 @@
-// 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.
-
-// +build appengine
-
-// App Engine hooks.
-
-package oauth2
-
-import (
-	"net/http"
-
-	"golang.org/x/net/context"
-	"golang.org/x/oauth2/internal"
-	"google.golang.org/appengine/urlfetch"
-)
-
-func init() {
-	internal.RegisterContextClientFunc(contextClientAppEngine)
-}
-
-func contextClientAppEngine(ctx context.Context) (*http.Client, error) {
-	return urlfetch.Client(ctx), nil
-}
diff --git a/vendor/golang.org/x/oauth2/internal/client_appengine.go b/vendor/golang.org/x/oauth2/internal/client_appengine.go
new file mode 100644
index 0000000000..7434871880
--- /dev/null
+++ b/vendor/golang.org/x/oauth2/internal/client_appengine.go
@@ -0,0 +1,13 @@
+// Copyright 2018 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.
+
+// +build appengine
+
+package internal
+
+import "google.golang.org/appengine/urlfetch"
+
+func init() {
+	appengineClientHook = urlfetch.Client
+}
diff --git a/vendor/golang.org/x/oauth2/internal/doc.go b/vendor/golang.org/x/oauth2/internal/doc.go
new file mode 100644
index 0000000000..03265e888a
--- /dev/null
+++ b/vendor/golang.org/x/oauth2/internal/doc.go
@@ -0,0 +1,6 @@
+// Copyright 2017 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 contains support packages for oauth2 package.
+package internal
diff --git a/vendor/golang.org/x/oauth2/internal/oauth2.go b/vendor/golang.org/x/oauth2/internal/oauth2.go
index fbe1028d64..c0ab196cf4 100644
--- a/vendor/golang.org/x/oauth2/internal/oauth2.go
+++ b/vendor/golang.org/x/oauth2/internal/oauth2.go
@@ -2,18 +2,14 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (
-	"bufio"
 	"crypto/rsa"
 	"crypto/x509"
 	"encoding/pem"
 	"errors"
 	"fmt"
-	"io"
-	"strings"
 )
 
 // ParseKey converts the binary contents of a private key file
@@ -30,7 +26,7 @@ func ParseKey(key []byte) (*rsa.PrivateKey, error) {
 	if err != nil {
 		parsedKey, err = x509.ParsePKCS1PrivateKey(key)
 		if err != nil {
-			return nil, fmt.Errorf("private key should be a PEM or plain PKSC1 or PKCS8; parse error: %v", err)
+			return nil, fmt.Errorf("private key should be a PEM or plain PKCS1 or PKCS8; parse error: %v", err)
 		}
 	}
 	parsed, ok := parsedKey.(*rsa.PrivateKey)
@@ -39,38 +35,3 @@ func ParseKey(key []byte) (*rsa.PrivateKey, error) {
 	}
 	return parsed, nil
 }
-
-func ParseINI(ini io.Reader) (map[string]map[string]string, error) {
-	result := map[string]map[string]string{
-		"": map[string]string{}, // root section
-	}
-	scanner := bufio.NewScanner(ini)
-	currentSection := ""
-	for scanner.Scan() {
-		line := strings.TrimSpace(scanner.Text())
-		if strings.HasPrefix(line, ";") {
-			// comment.
-			continue
-		}
-		if strings.HasPrefix(line, "[") && strings.HasSuffix(line, "]") {
-			currentSection = strings.TrimSpace(line[1 : len(line)-1])
-			result[currentSection] = map[string]string{}
-			continue
-		}
-		parts := strings.SplitN(line, "=", 2)
-		if len(parts) == 2 && parts[0] != "" {
-			result[currentSection][strings.TrimSpace(parts[0])] = strings.TrimSpace(parts[1])
-		}
-	}
-	if err := scanner.Err(); err != nil {
-		return nil, fmt.Errorf("error scanning ini: %v", err)
-	}
-	return result, nil
-}
-
-func CondVal(v string) []string {
-	if v == "" {
-		return nil
-	}
-	return []string{v}
-}
diff --git a/vendor/golang.org/x/oauth2/internal/token.go b/vendor/golang.org/x/oauth2/internal/token.go
index 18328a0dcf..5ab17b9a5f 100644
--- a/vendor/golang.org/x/oauth2/internal/token.go
+++ b/vendor/golang.org/x/oauth2/internal/token.go
@@ -2,11 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (
+	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -17,10 +18,10 @@ import (
 	"strings"
 	"time"
 
-	"golang.org/x/net/context"
+	"golang.org/x/net/context/ctxhttp"
 )
 
-// Token represents the crendentials used to authorize
+// Token represents the credentials used to authorize
 // the requests to access protected resources on the OAuth 2.0
 // provider's backend.
 //
@@ -91,6 +92,7 @@ func (e *expirationTime) UnmarshalJSON(b []byte) error {
 
 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/",
@@ -99,10 +101,16 @@ var brokenAuthHeaderProviders = []string{
 	"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/",
@@ -117,6 +125,24 @@ var brokenAuthHeaderProviders = []string{
 	"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",
+}
+
+// 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) {
@@ -139,6 +165,14 @@ func providerAuthHeaderWorks(tokenURL string) bool {
 		}
 	}
 
+	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
@@ -147,14 +181,14 @@ func providerAuthHeaderWorks(tokenURL string) bool {
 }
 
 func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string, v url.Values) (*Token, error) {
-	hc, err := ContextClient(ctx)
-	if err != nil {
-		return nil, err
-	}
-	v.Set("client_id", clientID)
 	bustedAuth := !providerAuthHeaderWorks(tokenURL)
-	if bustedAuth && clientSecret != "" {
-		v.Set("client_secret", clientSecret)
+	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 {
@@ -162,9 +196,9 @@ func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string,
 	}
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 	if !bustedAuth {
-		req.SetBasicAuth(clientID, clientSecret)
+		req.SetBasicAuth(url.QueryEscape(clientID), url.QueryEscape(clientSecret))
 	}
-	r, err := hc.Do(req)
+	r, err := ctxhttp.Do(ctx, ContextClient(ctx), req)
 	if err != nil {
 		return nil, err
 	}
@@ -174,7 +208,10 @@ func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string,
 		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
 	}
 	if code := r.StatusCode; code < 200 || code > 299 {
-		return nil, fmt.Errorf("oauth2: cannot fetch token: %v\nResponse: %s", r.Status, body)
+		return nil, &RetrieveError{
+			Response: r,
+			Body:     body,
+		}
 	}
 
 	var token *Token
@@ -221,5 +258,17 @@ func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string,
 	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)
+}
diff --git a/vendor/golang.org/x/oauth2/internal/transport.go b/vendor/golang.org/x/oauth2/internal/transport.go
index f1f173e345..572074a637 100644
--- a/vendor/golang.org/x/oauth2/internal/transport.go
+++ b/vendor/golang.org/x/oauth2/internal/transport.go
@@ -2,13 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package internal contains support packages for oauth2 package.
 package internal
 
 import (
+	"context"
 	"net/http"
-
-	"golang.org/x/net/context"
 )
 
 // HTTPClient is the context key to use with golang.org/x/net/context's
@@ -20,50 +18,16 @@ var HTTPClient ContextKey
 // because nobody else can create a ContextKey, being unexported.
 type ContextKey struct{}
 
-// ContextClientFunc is a func which tries to return an *http.Client
-// given a Context value. If it returns an error, the search stops
-// with that error.  If it returns (nil, nil), the search continues
-// down the list of registered funcs.
-type ContextClientFunc func(context.Context) (*http.Client, error)
-
-var contextClientFuncs []ContextClientFunc
-
-func RegisterContextClientFunc(fn ContextClientFunc) {
-	contextClientFuncs = append(contextClientFuncs, fn)
-}
+var appengineClientHook func(context.Context) *http.Client
 
-func ContextClient(ctx context.Context) (*http.Client, error) {
+func ContextClient(ctx context.Context) *http.Client {
 	if ctx != nil {
 		if hc, ok := ctx.Value(HTTPClient).(*http.Client); ok {
-			return hc, nil
-		}
-	}
-	for _, fn := range contextClientFuncs {
-		c, err := fn(ctx)
-		if err != nil {
-			return nil, err
-		}
-		if c != nil {
-			return c, nil
+			return hc
 		}
 	}
-	return http.DefaultClient, nil
-}
-
-func ContextTransport(ctx context.Context) http.RoundTripper {
-	hc, err := ContextClient(ctx)
-	// This is a rare error case (somebody using nil on App Engine).
-	if err != nil {
-		return ErrorTransport{err}
+	if appengineClientHook != nil {
+		return appengineClientHook(ctx)
 	}
-	return hc.Transport
-}
-
-// ErrorTransport returns the specified error on RoundTrip.
-// This RoundTripper should be used in rare error cases where
-// error handling can be postponed to response handling time.
-type ErrorTransport struct{ Err error }
-
-func (t ErrorTransport) RoundTrip(*http.Request) (*http.Response, error) {
-	return nil, t.Err
+	return http.DefaultClient
 }
diff --git a/vendor/golang.org/x/oauth2/oauth2.go b/vendor/golang.org/x/oauth2/oauth2.go
index 7b06bfe1ef..0a3c1e1632 100644
--- a/vendor/golang.org/x/oauth2/oauth2.go
+++ b/vendor/golang.org/x/oauth2/oauth2.go
@@ -3,19 +3,20 @@
 // license that can be found in the LICENSE file.
 
 // Package oauth2 provides support for making
-// OAuth2 authorized and authenticated HTTP requests.
+// OAuth2 authorized and authenticated HTTP requests,
+// as specified in RFC 6749.
 // It can additionally grant authorization with Bearer JWT.
 package oauth2 // import "golang.org/x/oauth2"
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"net/http"
 	"net/url"
 	"strings"
 	"sync"
 
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2/internal"
 )
 
@@ -117,21 +118,30 @@ func SetAuthURLParam(key, value string) AuthCodeOption {
 // that asks for permissions for the required scopes explicitly.
 //
 // State is a token to protect the user from CSRF attacks. You must
-// always provide a non-zero string and validate that it matches the
+// always provide a non-empty string and validate that it matches the
 // the state query parameter on your redirect callback.
 // See http://tools.ietf.org/html/rfc6749#section-10.12 for more info.
 //
 // Opts may include AccessTypeOnline or AccessTypeOffline, as well
 // as ApprovalForce.
+// It can also be used to pass the PKCE challange.
+// See https://www.oauth.com/oauth2-servers/pkce/ for more info.
 func (c *Config) AuthCodeURL(state string, opts ...AuthCodeOption) string {
 	var buf bytes.Buffer
 	buf.WriteString(c.Endpoint.AuthURL)
 	v := url.Values{
 		"response_type": {"code"},
 		"client_id":     {c.ClientID},
-		"redirect_uri":  internal.CondVal(c.RedirectURL),
-		"scope":         internal.CondVal(strings.Join(c.Scopes, " ")),
-		"state":         internal.CondVal(state),
+	}
+	if c.RedirectURL != "" {
+		v.Set("redirect_uri", c.RedirectURL)
+	}
+	if len(c.Scopes) > 0 {
+		v.Set("scope", strings.Join(c.Scopes, " "))
+	}
+	if state != "" {
+		// TODO(light): Docs say never to omit state; don't allow empty.
+		v.Set("state", state)
 	}
 	for _, opt := range opts {
 		opt.setValue(v)
@@ -157,12 +167,15 @@ func (c *Config) AuthCodeURL(state string, opts ...AuthCodeOption) string {
 // The HTTP client to use is derived from the context.
 // If nil, http.DefaultClient is used.
 func (c *Config) PasswordCredentialsToken(ctx context.Context, username, password string) (*Token, error) {
-	return retrieveToken(ctx, c, url.Values{
+	v := url.Values{
 		"grant_type": {"password"},
 		"username":   {username},
 		"password":   {password},
-		"scope":      internal.CondVal(strings.Join(c.Scopes, " ")),
-	})
+	}
+	if len(c.Scopes) > 0 {
+		v.Set("scope", strings.Join(c.Scopes, " "))
+	}
+	return retrieveToken(ctx, c, v)
 }
 
 // Exchange converts an authorization code into a token.
@@ -175,13 +188,21 @@ func (c *Config) PasswordCredentialsToken(ctx context.Context, username, passwor
 //
 // The code will be in the *http.Request.FormValue("code"). Before
 // calling Exchange, be sure to validate FormValue("state").
-func (c *Config) Exchange(ctx context.Context, code string) (*Token, error) {
-	return retrieveToken(ctx, c, url.Values{
-		"grant_type":   {"authorization_code"},
-		"code":         {code},
-		"redirect_uri": internal.CondVal(c.RedirectURL),
-		"scope":        internal.CondVal(strings.Join(c.Scopes, " ")),
-	})
+//
+// Opts may include the PKCE verifier code if previously used in AuthCodeURL.
+// See https://www.oauth.com/oauth2-servers/pkce/ for more info.
+func (c *Config) Exchange(ctx context.Context, code string, opts ...AuthCodeOption) (*Token, error) {
+	v := url.Values{
+		"grant_type": {"authorization_code"},
+		"code":       {code},
+	}
+	if c.RedirectURL != "" {
+		v.Set("redirect_uri", c.RedirectURL)
+	}
+	for _, opt := range opts {
+		opt.setValue(v)
+	}
+	return retrieveToken(ctx, c, v)
 }
 
 // Client returns an HTTP client using the provided token.
@@ -292,20 +313,20 @@ var HTTPClient internal.ContextKey
 // NewClient creates an *http.Client from a Context and TokenSource.
 // The returned client is not valid beyond the lifetime of the context.
 //
+// Note that if a custom *http.Client is provided via the Context it
+// is used only for token acquisition and is not used to configure the
+// *http.Client returned from NewClient.
+//
 // As a special case, if src is nil, a non-OAuth2 client is returned
 // using the provided context. This exists to support related OAuth2
 // packages.
 func NewClient(ctx context.Context, src TokenSource) *http.Client {
 	if src == nil {
-		c, err := internal.ContextClient(ctx)
-		if err != nil {
-			return &http.Client{Transport: internal.ErrorTransport{Err: err}}
-		}
-		return c
+		return internal.ContextClient(ctx)
 	}
 	return &http.Client{
 		Transport: &Transport{
-			Base:   internal.ContextTransport(ctx),
+			Base:   internal.ContextClient(ctx).Transport,
 			Source: ReuseTokenSource(nil, src),
 		},
 	}
diff --git a/vendor/golang.org/x/oauth2/token.go b/vendor/golang.org/x/oauth2/token.go
index 7a3167f15b..9be1ae5373 100644
--- a/vendor/golang.org/x/oauth2/token.go
+++ b/vendor/golang.org/x/oauth2/token.go
@@ -5,13 +5,14 @@
 package oauth2
 
 import (
+	"context"
+	"fmt"
 	"net/http"
 	"net/url"
 	"strconv"
 	"strings"
 	"time"
 
-	"golang.org/x/net/context"
 	"golang.org/x/oauth2/internal"
 )
 
@@ -20,7 +21,7 @@ import (
 // expirations due to client-server time mismatches.
 const expiryDelta = 10 * time.Second
 
-// Token represents the crendentials used to authorize
+// Token represents the credentials used to authorize
 // the requests to access protected resources on the OAuth 2.0
 // provider's backend.
 //
@@ -123,7 +124,7 @@ func (t *Token) expired() bool {
 	if t.Expiry.IsZero() {
 		return false
 	}
-	return t.Expiry.Add(-expiryDelta).Before(time.Now())
+	return t.Expiry.Round(0).Add(-expiryDelta).Before(time.Now())
 }
 
 // Valid reports whether t is non-nil, has an AccessToken, and is not expired.
@@ -152,7 +153,23 @@ func tokenFromInternal(t *internal.Token) *Token {
 func retrieveToken(ctx context.Context, c *Config, v url.Values) (*Token, error) {
 	tk, err := internal.RetrieveToken(ctx, c.ClientID, c.ClientSecret, c.Endpoint.TokenURL, v)
 	if err != nil {
+		if rErr, ok := err.(*internal.RetrieveError); ok {
+			return nil, (*RetrieveError)(rErr)
+		}
 		return nil, err
 	}
 	return tokenFromInternal(tk), nil
 }
+
+// RetrieveError is the error returned when the token endpoint returns a
+// non-2XX HTTP status code.
+type RetrieveError struct {
+	Response *http.Response
+	// Body is the body that was consumed by reading Response.Body.
+	// It may be truncated.
+	Body []byte
+}
+
+func (r *RetrieveError) Error() string {
+	return fmt.Sprintf("oauth2: cannot fetch token: %v\nResponse: %s", r.Response.Status, r.Body)
+}
diff --git a/vendor/golang.org/x/oauth2/transport.go b/vendor/golang.org/x/oauth2/transport.go
index 92ac7e2531..aa0d34f1e0 100644
--- a/vendor/golang.org/x/oauth2/transport.go
+++ b/vendor/golang.org/x/oauth2/transport.go
@@ -31,9 +31,17 @@ type Transport struct {
 }
 
 // RoundTrip authorizes and authenticates the request with an
-// access token. If no token exists or token is expired,
-// tries to refresh/fetch a new token.
+// access token from Transport's Source.
 func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
+	reqBodyClosed := false
+	if req.Body != nil {
+		defer func() {
+			if !reqBodyClosed {
+				req.Body.Close()
+			}
+		}()
+	}
+
 	if t.Source == nil {
 		return nil, errors.New("oauth2: Transport's Source is nil")
 	}
@@ -46,6 +54,10 @@ func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 	token.SetAuthHeader(req2)
 	t.setModReq(req, req2)
 	res, err := t.base().RoundTrip(req2)
+
+	// req.Body is assumed to have been closed by the base RoundTripper.
+	reqBodyClosed = true
+
 	if err != nil {
 		t.setModReq(req, nil)
 		return nil, err