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diff --git a/vendor/golang.org/x/oauth2/oauth2.go b/vendor/golang.org/x/oauth2/oauth2.go
new file mode 100644
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+++ b/vendor/golang.org/x/oauth2/oauth2.go
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+// 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 provides support for making
+// 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/oauth2/internal"
+)
+
+// NoContext is the default context you should supply if not using
+// your own context.Context (see https://golang.org/x/net/context).
+//
+// Deprecated: Use context.Background() or context.TODO() instead.
+var NoContext = context.TODO()
+
+// RegisterBrokenAuthHeaderProvider previously did something. It is now a no-op.
+//
+// Deprecated: this function no longer does anything. Caller code that
+// wants to avoid potential extra HTTP requests made during
+// auto-probing of the provider's auth style should set
+// Endpoint.AuthStyle.
+func RegisterBrokenAuthHeaderProvider(tokenURL string) {}
+
+// Config describes a typical 3-legged OAuth2 flow, with both the
+// client application information and the server's endpoint URLs.
+// For the client credentials 2-legged OAuth2 flow, see the clientcredentials
+// package (https://golang.org/x/oauth2/clientcredentials).
+type Config struct {
+	// ClientID is the application's ID.
+	ClientID string
+
+	// ClientSecret is the application's secret.
+	ClientSecret string
+
+	// Endpoint contains the resource server's token endpoint
+	// URLs. These are constants specific to each server and are
+	// often available via site-specific packages, such as
+	// google.Endpoint or github.Endpoint.
+	Endpoint Endpoint
+
+	// RedirectURL is the URL to redirect users going through
+	// the OAuth flow, after the resource owner's URLs.
+	RedirectURL string
+
+	// Scope specifies optional requested permissions.
+	Scopes []string
+}
+
+// A TokenSource is anything that can return a token.
+type TokenSource interface {
+	// Token returns a token or an error.
+	// Token must be safe for concurrent use by multiple goroutines.
+	// The returned Token must not be modified.
+	Token() (*Token, error)
+}
+
+// Endpoint represents an OAuth 2.0 provider's authorization and token
+// endpoint URLs.
+type Endpoint struct {
+	AuthURL  string
+	TokenURL string
+
+	// AuthStyle optionally specifies how the endpoint wants the
+	// client ID & client secret sent. The zero value means to
+	// auto-detect.
+	AuthStyle AuthStyle
+}
+
+// AuthStyle represents how requests for tokens are authenticated
+// to the server.
+type AuthStyle int
+
+const (
+	// AuthStyleAutoDetect means to auto-detect which authentication
+	// style the provider wants by trying both ways and caching
+	// the successful way for the future.
+	AuthStyleAutoDetect AuthStyle = 0
+
+	// AuthStyleInParams sends the "client_id" and "client_secret"
+	// in the POST body as application/x-www-form-urlencoded parameters.
+	AuthStyleInParams AuthStyle = 1
+
+	// AuthStyleInHeader sends the client_id and client_password
+	// using HTTP Basic Authorization. This is an optional style
+	// described in the OAuth2 RFC 6749 section 2.3.1.
+	AuthStyleInHeader AuthStyle = 2
+)
+
+var (
+	// AccessTypeOnline and AccessTypeOffline are options passed
+	// to the Options.AuthCodeURL method. They modify the
+	// "access_type" field that gets sent in the URL returned by
+	// AuthCodeURL.
+	//
+	// Online is the default if neither is specified. If your
+	// application needs to refresh access tokens when the user
+	// is not present at the browser, then use offline. This will
+	// result in your application obtaining a refresh token the
+	// first time your application exchanges an authorization
+	// code for a user.
+	AccessTypeOnline  AuthCodeOption = SetAuthURLParam("access_type", "online")
+	AccessTypeOffline AuthCodeOption = SetAuthURLParam("access_type", "offline")
+
+	// ApprovalForce forces the users to view the consent dialog
+	// and confirm the permissions request at the URL returned
+	// from AuthCodeURL, even if they've already done so.
+	ApprovalForce AuthCodeOption = SetAuthURLParam("prompt", "consent")
+)
+
+// An AuthCodeOption is passed to Config.AuthCodeURL.
+type AuthCodeOption interface {
+	setValue(url.Values)
+}
+
+type setParam struct{ k, v string }
+
+func (p setParam) setValue(m url.Values) { m.Set(p.k, p.v) }
+
+// SetAuthURLParam builds an AuthCodeOption which passes key/value parameters
+// to a provider's authorization endpoint.
+func SetAuthURLParam(key, value string) AuthCodeOption {
+	return setParam{key, value}
+}
+
+// AuthCodeURL returns a URL to OAuth 2.0 provider's consent page
+// 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-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 challenge.
+// 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},
+	}
+	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)
+	}
+	if strings.Contains(c.Endpoint.AuthURL, "?") {
+		buf.WriteByte('&')
+	} else {
+		buf.WriteByte('?')
+	}
+	buf.WriteString(v.Encode())
+	return buf.String()
+}
+
+// PasswordCredentialsToken converts a resource owner username and password
+// pair into a token.
+//
+// Per the RFC, this grant type should only be used "when there is a high
+// degree of trust between the resource owner and the client (e.g., the client
+// is part of the device operating system or a highly privileged application),
+// and when other authorization grant types are not available."
+// See https://tools.ietf.org/html/rfc6749#section-4.3 for more info.
+//
+// The provided context optionally controls which HTTP client is used. See the HTTPClient variable.
+func (c *Config) PasswordCredentialsToken(ctx context.Context, username, password string) (*Token, error) {
+	v := url.Values{
+		"grant_type": {"password"},
+		"username":   {username},
+		"password":   {password},
+	}
+	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.
+//
+// It is used after a resource provider redirects the user back
+// to the Redirect URI (the URL obtained from AuthCodeURL).
+//
+// The provided context optionally controls which HTTP client is used. See the HTTPClient variable.
+//
+// The code will be in the *http.Request.FormValue("code"). Before
+// calling Exchange, be sure to validate FormValue("state").
+//
+// 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.
+// The token will auto-refresh as necessary. The underlying
+// HTTP transport will be obtained using the provided context.
+// The returned client and its Transport should not be modified.
+func (c *Config) Client(ctx context.Context, t *Token) *http.Client {
+	return NewClient(ctx, c.TokenSource(ctx, t))
+}
+
+// TokenSource returns a TokenSource that returns t until t expires,
+// automatically refreshing it as necessary using the provided context.
+//
+// Most users will use Config.Client instead.
+func (c *Config) TokenSource(ctx context.Context, t *Token) TokenSource {
+	tkr := &tokenRefresher{
+		ctx:  ctx,
+		conf: c,
+	}
+	if t != nil {
+		tkr.refreshToken = t.RefreshToken
+	}
+	return &reuseTokenSource{
+		t:   t,
+		new: tkr,
+	}
+}
+
+// tokenRefresher is a TokenSource that makes "grant_type"=="refresh_token"
+// HTTP requests to renew a token using a RefreshToken.
+type tokenRefresher struct {
+	ctx          context.Context // used to get HTTP requests
+	conf         *Config
+	refreshToken string
+}
+
+// WARNING: Token is not safe for concurrent access, as it
+// updates the tokenRefresher's refreshToken field.
+// Within this package, it is used by reuseTokenSource which
+// synchronizes calls to this method with its own mutex.
+func (tf *tokenRefresher) Token() (*Token, error) {
+	if tf.refreshToken == "" {
+		return nil, errors.New("oauth2: token expired and refresh token is not set")
+	}
+
+	tk, err := retrieveToken(tf.ctx, tf.conf, url.Values{
+		"grant_type":    {"refresh_token"},
+		"refresh_token": {tf.refreshToken},
+	})
+
+	if err != nil {
+		return nil, err
+	}
+	if tf.refreshToken != tk.RefreshToken {
+		tf.refreshToken = tk.RefreshToken
+	}
+	return tk, err
+}
+
+// reuseTokenSource is a TokenSource that holds a single token in memory
+// and validates its expiry before each call to retrieve it with
+// Token. If it's expired, it will be auto-refreshed using the
+// new TokenSource.
+type reuseTokenSource struct {
+	new TokenSource // called when t is expired.
+
+	mu sync.Mutex // guards t
+	t  *Token
+}
+
+// Token returns the current token if it's still valid, else will
+// refresh the current token (using r.Context for HTTP client
+// information) and return the new one.
+func (s *reuseTokenSource) Token() (*Token, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.t.Valid() {
+		return s.t, nil
+	}
+	t, err := s.new.Token()
+	if err != nil {
+		return nil, err
+	}
+	s.t = t
+	return t, nil
+}
+
+// StaticTokenSource returns a TokenSource that always returns the same token.
+// Because the provided token t is never refreshed, StaticTokenSource is only
+// useful for tokens that never expire.
+func StaticTokenSource(t *Token) TokenSource {
+	return staticTokenSource{t}
+}
+
+// staticTokenSource is a TokenSource that always returns the same Token.
+type staticTokenSource struct {
+	t *Token
+}
+
+func (s staticTokenSource) Token() (*Token, error) {
+	return s.t, nil
+}
+
+// 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 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 {
+		return internal.ContextClient(ctx)
+	}
+	return &http.Client{
+		Transport: &Transport{
+			Base:   internal.ContextClient(ctx).Transport,
+			Source: ReuseTokenSource(nil, src),
+		},
+	}
+}
+
+// ReuseTokenSource returns a TokenSource which repeatedly returns the
+// same token as long as it's valid, starting with t.
+// When its cached token is invalid, a new token is obtained from src.
+//
+// ReuseTokenSource is typically used to reuse tokens from a cache
+// (such as a file on disk) between runs of a program, rather than
+// obtaining new tokens unnecessarily.
+//
+// The initial token t may be nil, in which case the TokenSource is
+// wrapped in a caching version if it isn't one already. This also
+// means it's always safe to wrap ReuseTokenSource around any other
+// TokenSource without adverse effects.
+func ReuseTokenSource(t *Token, src TokenSource) TokenSource {
+	// Don't wrap a reuseTokenSource in itself. That would work,
+	// but cause an unnecessary number of mutex operations.
+	// Just build the equivalent one.
+	if rt, ok := src.(*reuseTokenSource); ok {
+		if t == nil {
+			// Just use it directly.
+			return rt
+		}
+		src = rt.new
+	}
+	return &reuseTokenSource{
+		t:   t,
+		new: src,
+	}
+}