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/facebook/facebook.go

@@ -0,0 +1,195 @@
+// Package facebook implements the OAuth2 protocol for authenticating users through Facebook.
+// This package can be used as a reference implementation of an OAuth2 provider for Goth.
+package facebook
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+
+	"github.com/markbates/goth"
+	"golang.org/x/oauth2"
+	"fmt"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+)
+
+const (
+	authURL         string = "https://www.facebook.com/dialog/oauth"
+	tokenURL        string = "https://graph.facebook.com/oauth/access_token"
+	endpointProfile string = "https://graph.facebook.com/me?fields=email,first_name,last_name,link,about,id,name,picture,location"
+)
+
+// New creates a new Facebook provider, and sets up important connection details.
+// You should always call `facebook.New` to get a new Provider. Never try to create
+// one manually.
+func New(clientKey, secret, callbackURL string, scopes ...string) *Provider {
+	p := &Provider{
+		ClientKey:           clientKey,
+		Secret:              secret,
+		CallbackURL:         callbackURL,
+		providerName:        "facebook",
+	}
+	p.config = newConfig(p, scopes)
+	return p
+}
+
+// Provider is the implementation of `goth.Provider` for accessing Facebook.
+type Provider struct {
+	ClientKey    string
+	Secret       string
+	CallbackURL  string
+	HTTPClient   *http.Client
+	config       *oauth2.Config
+	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 is a no-op for the facebook package.
+func (p *Provider) Debug(debug bool) {}
+
+// BeginAuth asks Facebook for an authentication end-point.
+func (p *Provider) BeginAuth(state string) (goth.Session, error) {
+	url := p.config.AuthCodeURL(state)
+	session := &Session{
+		AuthURL: url,
+	}
+	return session, nil
+}
+
+// FetchUser will go to Facebook and access basic information about the user.
+func (p *Provider) FetchUser(session goth.Session) (goth.User, error) {
+	sess := session.(*Session)
+	user := goth.User{
+		AccessToken: sess.AccessToken,
+		Provider:    p.Name(),
+		ExpiresAt:   sess.ExpiresAt,
+	}
+
+	if user.AccessToken == "" {
+		// data is not yet retrieved since accessToken is still empty
+		return user, fmt.Errorf("%s cannot get user information without accessToken", p.providerName)
+	}
+
+	// always add appsecretProof to make calls more protected
+	// https://github.com/markbates/goth/issues/96
+	// https://developers.facebook.com/docs/graph-api/securing-requests
+	hash := hmac.New(sha256.New, []byte(p.Secret))
+	hash.Write([]byte(sess.AccessToken))
+	appsecretProof := hex.EncodeToString(hash.Sum(nil))
+
+	response, err := p.Client().Get(endpointProfile + "&access_token=" + url.QueryEscape(sess.AccessToken) + "&appsecret_proof=" + appsecretProof)
+	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)
+	if err != nil {
+		return user, err
+	}
+
+	err = json.NewDecoder(bytes.NewReader(bits)).Decode(&user.RawData)
+	if err != nil {
+		return user, err
+	}
+
+	err = userFromReader(bytes.NewReader(bits), &user)
+	return user, err
+}
+
+func userFromReader(reader io.Reader, user *goth.User) error {
+	u := struct {
+		ID        string `json:"id"`
+		Email     string `json:"email"`
+		About     string `json:"about"`
+		Name      string `json:"name"`
+		FirstName string `json:"first_name"`
+		LastName  string `json:"last_name"`
+		Link      string `json:"link"`
+		Picture struct {
+			Data struct {
+				URL string `json:"url"`
+			} `json:"data"`
+		} `json:"picture"`
+		Location struct {
+			Name string `json:"name"`
+		} `json:"location"`
+	}{}
+
+	err := json.NewDecoder(reader).Decode(&u)
+	if err != nil {
+		return err
+	}
+
+	user.Name = u.Name
+	user.FirstName = u.FirstName
+	user.LastName = u.LastName
+	user.NickName = u.Name
+	user.Email = u.Email
+	user.Description = u.About
+	user.AvatarURL = u.Picture.Data.URL
+	user.UserID = u.ID
+	user.Location = u.Location.Name
+
+	return err
+}
+
+func newConfig(provider *Provider, scopes []string) *oauth2.Config {
+	c := &oauth2.Config{
+		ClientID:     provider.ClientKey,
+		ClientSecret: provider.Secret,
+		RedirectURL:  provider.CallbackURL,
+		Endpoint: oauth2.Endpoint{
+			AuthURL:  authURL,
+			TokenURL: tokenURL,
+		},
+		Scopes: []string{
+			"email",
+		},
+	}
+
+	defaultScopes := map[string]struct{}{
+		"email": {},
+	}
+
+	for _, scope := range scopes {
+		if _, exists := defaultScopes[scope]; !exists {
+			c.Scopes = append(c.Scopes, scope)
+		}
+	}
+
+	return c
+}
+
+//RefreshToken refresh token is not provided by facebook
+func (p *Provider) RefreshToken(refreshToken string) (*oauth2.Token, error) {
+	return nil, errors.New("Refresh token is not provided by facebook")
+}
+
+//RefreshTokenAvailable refresh token is not provided by facebook
+func (p *Provider) RefreshTokenAvailable() bool {
+	return false
+}