Additional OAuth2 providers (#1010)

* add google+

* sort signin oauth2 providers based on the name so order is always the same

* update auth tip for google+

* add gitlab provider

* add bitbucket provider (and some go fmt)

* add twitter provider

* add facebook provider

* add dropbox provider

* add openid connect provider incl. new format of tips section in "Add New Source"

* lower the amount of disk storage for each session to prevent issues while building cross platform (and disk overflow)

* imports according to goimport and code style

* make it possible to set custom urls to gitlab and github provider (only these could have a different host)

* split up oauth2 into multiple files

* small typo in comment

* fix indention

* fix indentation

* fix new line before external import

* fix layout of signin part

* update "broken" dependency

vendor/github.com/markbates/goth/providers/twitter/twitter.go

@@ -0,0 +1,160 @@
+// Package twitter implements the OAuth protocol for authenticating users through Twitter.
+// This package can be used as a reference implementation of an OAuth provider for Goth.
+package twitter
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/markbates/goth"
+	"github.com/mrjones/oauth"
+	"golang.org/x/oauth2"
+	"fmt"
+)
+
+var (
+	requestURL      = "https://api.twitter.com/oauth/request_token"
+	authorizeURL    = "https://api.twitter.com/oauth/authorize"
+	authenticateURL = "https://api.twitter.com/oauth/authenticate"
+	tokenURL        = "https://api.twitter.com/oauth/access_token"
+	endpointProfile = "https://api.twitter.com/1.1/account/verify_credentials.json"
+)
+
+// New creates a new Twitter provider, and sets up important connection details.
+// You should always call `twitter.New` to get a new Provider. Never try to create
+// one manually.
+//
+// If you'd like to use authenticate instead of authorize, use NewAuthenticate instead.
+func New(clientKey, secret, callbackURL string) *Provider {
+	p := &Provider{
+		ClientKey:           clientKey,
+		Secret:              secret,
+		CallbackURL:         callbackURL,
+		providerName:        "twitter",
+	}
+	p.consumer = newConsumer(p, authorizeURL)
+	return p
+}
+
+// NewAuthenticate is the almost same as New.
+// NewAuthenticate uses the authenticate URL instead of the authorize URL.
+func NewAuthenticate(clientKey, secret, callbackURL string) *Provider {
+	p := &Provider{
+		ClientKey:           clientKey,
+		Secret:              secret,
+		CallbackURL:         callbackURL,
+		providerName:        "twitter",
+	}
+	p.consumer = newConsumer(p, authenticateURL)
+	return p
+}
+
+// Provider is the implementation of `goth.Provider` for accessing Twitter.
+type Provider struct {
+	ClientKey    string
+	Secret       string
+	CallbackURL  string
+	HTTPClient   *http.Client
+	debug        bool
+	consumer     *oauth.Consumer
+	providerName string
+}
+
+// Name is the name used to retrieve this provider later.
+func (p *Provider) Name() string {
+	return p.providerName
+}
+
+// SetName is to update the name of the provider (needed in case of multiple providers of 1 type)
+func (p *Provider) SetName(name string) {
+	p.providerName = name
+}
+
+func (p *Provider) Client() *http.Client {
+	return goth.HTTPClientWithFallBack(p.HTTPClient)
+}
+
+// Debug sets the logging of the OAuth client to verbose.
+func (p *Provider) Debug(debug bool) {
+	p.debug = debug
+}
+
+// BeginAuth asks Twitter for an authentication end-point and a request token for a session.
+// Twitter does not support the "state" variable.
+func (p *Provider) BeginAuth(state string) (goth.Session, error) {
+	requestToken, url, err := p.consumer.GetRequestTokenAndUrl(p.CallbackURL)
+	session := &Session{
+		AuthURL:      url,
+		RequestToken: requestToken,
+	}
+	return session, err
+}
+
+// FetchUser will go to Twitter and access basic information about the user.
+func (p *Provider) FetchUser(session goth.Session) (goth.User, error) {
+	sess := session.(*Session)
+	user := goth.User{
+		Provider: p.Name(),
+	}
+
+	if sess.AccessToken == nil {
+		// data is not yet retrieved since accessToken is still empty
+		return user, fmt.Errorf("%s cannot get user information without accessToken", p.providerName)
+	}
+
+	response, err := p.consumer.Get(
+		endpointProfile,
+		map[string]string{"include_entities": "false", "skip_status": "true"},
+		sess.AccessToken)
+	if err != nil {
+		return user, err
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode != http.StatusOK {
+		return user, fmt.Errorf("%s responded with a %d trying to fetch user information", p.providerName, response.StatusCode)
+	}
+
+	bits, err := ioutil.ReadAll(response.Body)
+	err = json.NewDecoder(bytes.NewReader(bits)).Decode(&user.RawData)
+	if err != nil {
+		return user, err
+	}
+
+	user.Name = user.RawData["name"].(string)
+	user.NickName = user.RawData["screen_name"].(string)
+	user.Description = user.RawData["description"].(string)
+	user.AvatarURL = user.RawData["profile_image_url"].(string)
+	user.UserID = user.RawData["id_str"].(string)
+	user.Location = user.RawData["location"].(string)
+	user.AccessToken = sess.AccessToken.Token
+	user.AccessTokenSecret = sess.AccessToken.Secret
+	return user, err
+}
+
+func newConsumer(provider *Provider, authURL string) *oauth.Consumer {
+	c := oauth.NewConsumer(
+		provider.ClientKey,
+		provider.Secret,
+		oauth.ServiceProvider{
+			RequestTokenUrl:   requestURL,
+			AuthorizeTokenUrl: authURL,
+			AccessTokenUrl:    tokenURL,
+		})
+
+	c.Debug(provider.debug)
+	return c
+}
+
+//RefreshToken refresh token is not provided by twitter
+func (p *Provider) RefreshToken(refreshToken string) (*oauth2.Token, error) {
+	return nil, errors.New("Refresh token is not provided by twitter")
+}
+
+//RefreshTokenAvailable refresh token is not provided by twitter
+func (p *Provider) RefreshTokenAvailable() bool {
+	return false
+}