Oauth2 consumer (#679)

* initial stuff for oauth2 login, fails on:
* login button on the signIn page to start the OAuth2 flow and a callback for each provider
Only GitHub is implemented for now
* show login button only when the OAuth2 consumer is configured (and activated)
* create macaron group for oauth2 urls
* prevent net/http in modules (other then oauth2)
* use a new data sessions oauth2 folder for storing the oauth2 session data
* add missing 2FA when this is enabled on the user
* add password option for OAuth2 user , for use with git over http and login to the GUI
* add tip for registering a GitHub OAuth application
* at startup of Gitea register all configured providers and also on adding/deleting of new providers
* custom handling of errors in oauth2 request init + show better tip
* add ExternalLoginUser model and migration script to add it to database
* link a external account to an existing account (still need to handle wrong login and signup) and remove if user is removed
* remove the linked external account from the user his settings
* if user is unknown we allow him to register a new account or link it to some existing account
* sign up with button on signin page (als change OAuth2Provider structure so we can store basic stuff about providers)

* from gorilla/sessions docs:
"Important Note: If you aren't using gorilla/mux, you need to wrap your handlers with context.ClearHandler as or else you will leak memory!"
(we're using gorilla/sessions for storing oauth2 sessions)

* use updated goth lib that now supports getting the OAuth2 user if the AccessToken is still valid instead of re-authenticating (prevent flooding the OAuth2 provider)

vendor/golang.org/x/oauth2/AUTHORS

@@ -0,0 +1,3 @@
+# This source code refers to The Go Authors for copyright purposes.
+# The master list of authors is in the main Go distribution,
+# visible at http://tip.golang.org/AUTHORS.

vendor/golang.org/x/oauth2/CONTRIBUTING.md

@@ -0,0 +1,31 @@
+# Contributing to Go
+
+Go is an open source project.
+
+It is the work of hundreds of contributors. We appreciate your help!
+
+
+## Filing issues
+
+When [filing an issue](https://github.com/golang/oauth2/issues), make sure to answer these five questions:
+
+1. What version of Go are you using (`go version`)?
+2. What operating system and processor architecture are you using?
+3. What did you do?
+4. What did you expect to see?
+5. What did you see instead?
+
+General questions should go to the [golang-nuts mailing list](https://groups.google.com/group/golang-nuts) instead of the issue tracker.
+The gophers there will answer or ask you to file an issue if you've tripped over a bug.
+
+## Contributing code
+
+Please read the [Contribution Guidelines](https://golang.org/doc/contribute.html)
+before sending patches.
+
+**We do not accept GitHub pull requests**
+(we use [Gerrit](https://code.google.com/p/gerrit/) instead for code review).
+
+Unless otherwise noted, the Go source files are distributed under
+the BSD-style license found in the LICENSE file.
+

vendor/golang.org/x/oauth2/CONTRIBUTORS

@@ -0,0 +1,3 @@
+# This source code was written by the Go contributors.
+# The master list of contributors is in the main Go distribution,
+# visible at http://tip.golang.org/CONTRIBUTORS.

vendor/golang.org/x/oauth2/LICENSE

@@ -0,0 +1,27 @@
+Copyright (c) 2009 The oauth2 Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/golang.org/x/oauth2/README.md

@@ -0,0 +1,65 @@
+# OAuth2 for Go
+
+[![Build Status](https://travis-ci.org/golang/oauth2.svg?branch=master)](https://travis-ci.org/golang/oauth2)
+[![GoDoc](https://godoc.org/golang.org/x/oauth2?status.svg)](https://godoc.org/golang.org/x/oauth2)
+
+oauth2 package contains a client implementation for OAuth 2.0 spec.
+
+## Installation
+
+~~~~
+go get golang.org/x/oauth2
+~~~~
+
+See godoc for further documentation and examples.
+
+* [godoc.org/golang.org/x/oauth2](http://godoc.org/golang.org/x/oauth2)
+* [godoc.org/golang.org/x/oauth2/google](http://godoc.org/golang.org/x/oauth2/google)
+
+
+## App Engine
+
+In change 96e89be (March 2015) we removed the `oauth2.Context2` type in favor
+of the [`context.Context`](https://golang.org/x/net/context#Context) type from
+the `golang.org/x/net/context` package
+
+This means its no longer possible to use the "Classic App Engine"
+`appengine.Context` type with the `oauth2` package. (You're using
+Classic App Engine if you import the package `"appengine"`.)
+
+To work around this, you may use the new `"google.golang.org/appengine"`
+package. This package has almost the same API as the `"appengine"` package,
+but it can be fetched with `go get` and used on "Managed VMs" and well as
+Classic App Engine.
+
+See the [new `appengine` package's readme](https://github.com/golang/appengine#updating-a-go-app-engine-app)
+for information on updating your app.
+
+If you don't want to update your entire app to use the new App Engine packages,
+you may use both sets of packages in parallel, using only the new packages
+with the `oauth2` package.
+
+	import (
+		"golang.org/x/net/context"
+		"golang.org/x/oauth2"
+		"golang.org/x/oauth2/google"
+		newappengine "google.golang.org/appengine"
+		newurlfetch "google.golang.org/appengine/urlfetch"
+
+		"appengine"
+	)
+
+	func handler(w http.ResponseWriter, r *http.Request) {
+		var c appengine.Context = appengine.NewContext(r)
+		c.Infof("Logging a message with the old package")
+
+		var ctx context.Context = newappengine.NewContext(r)
+		client := &http.Client{
+			Transport: &oauth2.Transport{
+				Source: google.AppEngineTokenSource(ctx, "scope"),
+				Base:   &newurlfetch.Transport{Context: ctx},
+			},
+		}
+		client.Get("...")
+	}
+

vendor/golang.org/x/oauth2/client_appengine.go

@@ -0,0 +1,25 @@
+// 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
+}

vendor/golang.org/x/oauth2/internal/oauth2.go

@@ -0,0 +1,76 @@
+// 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 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
+// to an *rsa.PrivateKey. It detects whether the private key is in a
+// PEM container or not. If so, it extracts the the private key
+// from PEM container before conversion. It only supports PEM
+// containers with no passphrase.
+func ParseKey(key []byte) (*rsa.PrivateKey, error) {
+	block, _ := pem.Decode(key)
+	if block != nil {
+		key = block.Bytes
+	}
+	parsedKey, err := x509.ParsePKCS8PrivateKey(key)
+	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)
+		}
+	}
+	parsed, ok := parsedKey.(*rsa.PrivateKey)
+	if !ok {
+		return nil, errors.New("private key is invalid")
+	}
+	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}
+}

vendor/golang.org/x/oauth2/internal/token.go

@@ -0,0 +1,227 @@
+// 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 contains support packages for oauth2 package.
+package internal
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"mime"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/net/context"
+)
+
+// Token represents the crendentials 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.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://app.box.com/",
+	"https://connect.stripe.com/",
+	"https://login.microsoftonline.com/",
+	"https://login.salesforce.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.codeswholesale.com/oauth/token",
+}
+
+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
+		}
+	}
+
+	// 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) {
+	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)
+	}
+	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(clientID, clientSecret)
+	}
+	r, err := hc.Do(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, fmt.Errorf("oauth2: cannot fetch token: %v\nResponse: %s", r.Status, 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")
+	}
+	return token, nil
+}

vendor/golang.org/x/oauth2/internal/transport.go

@@ -0,0 +1,69 @@
+// 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 contains support packages for oauth2 package.
+package internal
+
+import (
+	"net/http"
+
+	"golang.org/x/net/context"
+)
+
+// HTTPClient is the context key to use with golang.org/x/net/context's
+// WithValue function to associate an *http.Client value with a context.
+var HTTPClient ContextKey
+
+// ContextKey is just an empty struct. It exists so HTTPClient can be
+// an immutable public variable with a unique type. It's immutable
+// 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)
+}
+
+func ContextClient(ctx context.Context) (*http.Client, error) {
+	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 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}
+	}
+	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
+}

vendor/golang.org/x/oauth2/token.go

@@ -0,0 +1,158 @@
+// 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 oauth2
+
+import (
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/net/context"
+	"golang.org/x/oauth2/internal"
+)
+
+// expiryDelta determines how earlier a token should be considered
+// expired than its actual expiration time. It is used to avoid late
+// expirations due to client-server time mismatches.
+const expiryDelta = 10 * time.Second
+
+// Token represents the crendentials used to authorize
+// the requests to access protected resources on the OAuth 2.0
+// provider's backend.
+//
+// Most users of this package should not access fields of Token
+// directly. They're exported mostly for use by related packages
+// implementing derivative OAuth2 flows.
+type Token struct {
+	// AccessToken is the token that authorizes and authenticates
+	// the requests.
+	AccessToken string `json:"access_token"`
+
+	// TokenType is the type of token.
+	// The Type method returns either this or "Bearer", the default.
+	TokenType string `json:"token_type,omitempty"`
+
+	// 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 `json:"refresh_token,omitempty"`
+
+	// 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 `json:"expiry,omitempty"`
+
+	// raw optionally contains extra metadata from the server
+	// when updating a token.
+	raw interface{}
+}
+
+// Type returns t.TokenType if non-empty, else "Bearer".
+func (t *Token) Type() string {
+	if strings.EqualFold(t.TokenType, "bearer") {
+		return "Bearer"
+	}
+	if strings.EqualFold(t.TokenType, "mac") {
+		return "MAC"
+	}
+	if strings.EqualFold(t.TokenType, "basic") {
+		return "Basic"
+	}
+	if t.TokenType != "" {
+		return t.TokenType
+	}
+	return "Bearer"
+}
+
+// SetAuthHeader sets the Authorization header to r using the access
+// token in t.
+//
+// This method is unnecessary when using Transport or an HTTP Client
+// returned by this package.
+func (t *Token) SetAuthHeader(r *http.Request) {
+	r.Header.Set("Authorization", t.Type()+" "+t.AccessToken)
+}
+
+// WithExtra returns a new Token that's a clone of t, but using the
+// provided raw extra map. This is only intended for use by packages
+// implementing derivative OAuth2 flows.
+func (t *Token) WithExtra(extra interface{}) *Token {
+	t2 := new(Token)
+	*t2 = *t
+	t2.raw = extra
+	return t2
+}
+
+// Extra returns an extra field.
+// Extra fields are key-value pairs returned by the server as a
+// part of the token retrieval response.
+func (t *Token) Extra(key string) interface{} {
+	if raw, ok := t.raw.(map[string]interface{}); ok {
+		return raw[key]
+	}
+
+	vals, ok := t.raw.(url.Values)
+	if !ok {
+		return nil
+	}
+
+	v := vals.Get(key)
+	switch s := strings.TrimSpace(v); strings.Count(s, ".") {
+	case 0: // Contains no "."; try to parse as int
+		if i, err := strconv.ParseInt(s, 10, 64); err == nil {
+			return i
+		}
+	case 1: // Contains a single "."; try to parse as float
+		if f, err := strconv.ParseFloat(s, 64); err == nil {
+			return f
+		}
+	}
+
+	return v
+}
+
+// expired reports whether the token is expired.
+// t must be non-nil.
+func (t *Token) expired() bool {
+	if t.Expiry.IsZero() {
+		return false
+	}
+	return t.Expiry.Add(-expiryDelta).Before(time.Now())
+}
+
+// Valid reports whether t is non-nil, has an AccessToken, and is not expired.
+func (t *Token) Valid() bool {
+	return t != nil && t.AccessToken != "" && !t.expired()
+}
+
+// tokenFromInternal maps an *internal.Token struct into
+// a *Token struct.
+func tokenFromInternal(t *internal.Token) *Token {
+	if t == nil {
+		return nil
+	}
+	return &Token{
+		AccessToken:  t.AccessToken,
+		TokenType:    t.TokenType,
+		RefreshToken: t.RefreshToken,
+		Expiry:       t.Expiry,
+		raw:          t.Raw,
+	}
+}
+
+// retrieveToken takes a *Config and uses that to retrieve an *internal.Token.
+// This token is then mapped from *internal.Token into an *oauth2.Token which is returned along
+// with an error..
+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 {
+		return nil, err
+	}
+	return tokenFromInternal(tk), nil
+}

vendor/golang.org/x/oauth2/transport.go

@@ -0,0 +1,132 @@
+// 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 oauth2
+
+import (
+	"errors"
+	"io"
+	"net/http"
+	"sync"
+)
+
+// Transport is an http.RoundTripper that makes OAuth 2.0 HTTP requests,
+// wrapping a base RoundTripper and adding an Authorization header
+// with a token from the supplied Sources.
+//
+// Transport is a low-level mechanism. Most code will use the
+// higher-level Config.Client method instead.
+type Transport struct {
+	// Source supplies the token to add to outgoing requests'
+	// Authorization headers.
+	Source TokenSource
+
+	// Base is the base RoundTripper used to make HTTP requests.
+	// If nil, http.DefaultTransport is used.
+	Base http.RoundTripper
+
+	mu     sync.Mutex                      // guards modReq
+	modReq map[*http.Request]*http.Request // original -> modified
+}
+
+// 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.
+func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if t.Source == nil {
+		return nil, errors.New("oauth2: Transport's Source is nil")
+	}
+	token, err := t.Source.Token()
+	if err != nil {
+		return nil, err
+	}
+
+	req2 := cloneRequest(req) // per RoundTripper contract
+	token.SetAuthHeader(req2)
+	t.setModReq(req, req2)
+	res, err := t.base().RoundTrip(req2)
+	if err != nil {
+		t.setModReq(req, nil)
+		return nil, err
+	}
+	res.Body = &onEOFReader{
+		rc: res.Body,
+		fn: func() { t.setModReq(req, nil) },
+	}
+	return res, nil
+}
+
+// CancelRequest cancels an in-flight request by closing its connection.
+func (t *Transport) CancelRequest(req *http.Request) {
+	type canceler interface {
+		CancelRequest(*http.Request)
+	}
+	if cr, ok := t.base().(canceler); ok {
+		t.mu.Lock()
+		modReq := t.modReq[req]
+		delete(t.modReq, req)
+		t.mu.Unlock()
+		cr.CancelRequest(modReq)
+	}
+}
+
+func (t *Transport) base() http.RoundTripper {
+	if t.Base != nil {
+		return t.Base
+	}
+	return http.DefaultTransport
+}
+
+func (t *Transport) setModReq(orig, mod *http.Request) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if t.modReq == nil {
+		t.modReq = make(map[*http.Request]*http.Request)
+	}
+	if mod == nil {
+		delete(t.modReq, orig)
+	} else {
+		t.modReq[orig] = mod
+	}
+}
+
+// cloneRequest returns a clone of the provided *http.Request.
+// The clone is a shallow copy of the struct and its Header map.
+func cloneRequest(r *http.Request) *http.Request {
+	// shallow copy of the struct
+	r2 := new(http.Request)
+	*r2 = *r
+	// deep copy of the Header
+	r2.Header = make(http.Header, len(r.Header))
+	for k, s := range r.Header {
+		r2.Header[k] = append([]string(nil), s...)
+	}
+	return r2
+}
+
+type onEOFReader struct {
+	rc io.ReadCloser
+	fn func()
+}
+
+func (r *onEOFReader) Read(p []byte) (n int, err error) {
+	n, err = r.rc.Read(p)
+	if err == io.EOF {
+		r.runFunc()
+	}
+	return
+}
+
+func (r *onEOFReader) Close() error {
+	err := r.rc.Close()
+	r.runFunc()
+	return err
+}
+
+func (r *onEOFReader) runFunc() {
+	if fn := r.fn; fn != nil {
+		fn()
+		r.fn = nil
+	}
+}