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

@@ -0,0 +1,224 @@
+// Package github implements the OAuth2 protocol for authenticating users through Github.
+// This package can be used as a reference implementation of an OAuth2 provider for Goth.
+package github
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"github.com/markbates/goth"
+	"golang.org/x/oauth2"
+)
+
+// These vars define the Authentication, Token, and API URLS for GitHub. If
+// using GitHub enterprise you should change these values before calling New.
+//
+// Examples:
+//	github.AuthURL = "https://github.acme.com/login/oauth/authorize
+//	github.TokenURL = "https://github.acme.com/login/oauth/access_token
+//	github.ProfileURL = "https://github.acme.com/api/v3/user
+//	github.EmailURL = "https://github.acme.com/api/v3/user/emails
+var (
+	AuthURL    = "https://github.com/login/oauth/authorize"
+	TokenURL   = "https://github.com/login/oauth/access_token"
+	ProfileURL = "https://api.github.com/user"
+	EmailURL   = "https://api.github.com/user/emails"
+)
+
+// New creates a new Github provider, and sets up important connection details.
+// You should always call `github.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:        "github",
+	}
+	p.config = newConfig(p, scopes)
+	return p
+}
+
+// Provider is the implementation of `goth.Provider` for accessing Github.
+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 github package.
+func (p *Provider) Debug(debug bool) {}
+
+// BeginAuth asks Github 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 Github 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(),
+	}
+
+	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)
+	}
+
+	response, err := p.Client().Get(ProfileURL + "?access_token=" + url.QueryEscape(sess.AccessToken))
+	if err != nil {
+		return user, err
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode != http.StatusOK {
+		return user, fmt.Errorf("GitHub API responded with a %d trying to fetch user information", 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)
+	if err != nil {
+		return user, err
+	}
+
+	if user.Email == "" {
+		for _, scope := range p.config.Scopes {
+			if strings.TrimSpace(scope) == "user" || strings.TrimSpace(scope) == "user:email" {
+				user.Email, err = getPrivateMail(p, sess)
+				if err != nil {
+					return user, err
+				}
+				break
+			}
+		}
+	}
+	return user, err
+}
+
+func userFromReader(reader io.Reader, user *goth.User) error {
+	u := struct {
+		ID       int    `json:"id"`
+		Email    string `json:"email"`
+		Bio      string `json:"bio"`
+		Name     string `json:"name"`
+		Login    string `json:"login"`
+		Picture  string `json:"avatar_url"`
+		Location string `json:"location"`
+	}{}
+
+	err := json.NewDecoder(reader).Decode(&u)
+	if err != nil {
+		return err
+	}
+
+	user.Name = u.Name
+	user.NickName = u.Login
+	user.Email = u.Email
+	user.Description = u.Bio
+	user.AvatarURL = u.Picture
+	user.UserID = strconv.Itoa(u.ID)
+	user.Location = u.Location
+
+	return err
+}
+
+func getPrivateMail(p *Provider, sess *Session) (email string, err error) {
+	response, err := p.Client().Get(EmailURL + "?access_token=" + url.QueryEscape(sess.AccessToken))
+	if err != nil {
+		if response != nil {
+			response.Body.Close()
+		}
+		return email, err
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode != http.StatusOK {
+		return email, fmt.Errorf("GitHub API responded with a %d trying to fetch user email", response.StatusCode)
+	}
+
+	var mailList = []struct {
+		Email    string `json:"email"`
+		Primary  bool   `json:"primary"`
+		Verified bool   `json:"verified"`
+	}{}
+	err = json.NewDecoder(response.Body).Decode(&mailList)
+	if err != nil {
+		return email, err
+	}
+	for _, v := range mailList {
+		if v.Primary && v.Verified {
+			return v.Email, nil
+		}
+	}
+	// can't get primary email - shouldn't be possible
+	return
+}
+
+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{},
+	}
+
+	for _, scope := range scopes {
+		c.Scopes = append(c.Scopes, scope)
+	}
+
+	return c
+}
+
+//RefreshToken refresh token is not provided by github
+func (p *Provider) RefreshToken(refreshToken string) (*oauth2.Token, error) {
+	return nil, errors.New("Refresh token is not provided by github")
+}
+
+//RefreshTokenAvailable refresh token is not provided by github
+func (p *Provider) RefreshTokenAvailable() bool {
+	return false
+}