Facebook Authentication Provider

* will not re-prompt if the email permission is denied, or if you previously authorized the same FB app without the email scope.

README.md

@@ -30,6 +30,7 @@ Valid providers are :
 
 * [Google](#google-auth-provider) *default*
 * [Azure](#azure-auth-provider)
+* [Facebook](#facebook-auth-provider)
 * [GitHub](#github-auth-provider)
 * [GitLab](#gitlab-auth-provider)
 * [LinkedIn](#linkedin-auth-provider)
@@ -87,6 +88,11 @@ Note: The user is checked against the group members list on initial authenticati
 The Azure AD auth provider uses `openid` as it default scope. It uses `https://graph.windows.net` as a default protected resource. It call to `https://graph.windows.net/me` to get the email address of the user that logs in.
 
 
+### Facebook Auth Provider
+
+1. Create a new FB App from <https://developers.facebook.com/>
+2. Under FB Login, set your Valid OAuth redirect URIs to `https://internal.yourcompany.com/oauth2/callback`
+
 ### GitHub Auth Provider
 
 1. Create a new project: https://github.com/settings/developers

api/api.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -31,6 +32,24 @@ func Request(req *http.Request) (*simplejson.Json, error) {
 	return data, nil
 }
 
+func RequestJson(req *http.Request, v interface{}) error {
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		log.Printf("%s %s %s", req.Method, req.URL, err)
+		return err
+	}
+	body, err := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	log.Printf("%d %s %s %s", resp.StatusCode, req.Method, req.URL, body)
+	if err != nil {
+		return err
+	}
+	if resp.StatusCode != 200 {
+		return fmt.Errorf("got %d %s", resp.StatusCode, body)
+	}
+	return json.Unmarshal(body, v)
+}
+
 func RequestUnparsedResponse(url string, header http.Header) (resp *http.Response, err error) {
 	req, err := http.NewRequest("GET", url, nil)
 	if err != nil {

providers/facebook.go

@@ -0,0 +1,80 @@
+package providers
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"net/url"
+
+	"github.com/bitly/oauth2_proxy/api"
+)
+
+type FacebookProvider struct {
+	*ProviderData
+}
+
+func NewFacebookProvider(p *ProviderData) *FacebookProvider {
+	p.ProviderName = "Facebook"
+	if p.LoginURL.String() == "" {
+		p.LoginURL = &url.URL{Scheme: "https",
+			Host: "www.facebook.com",
+			Path: "/v2.5/dialog/oauth",
+			// ?granted_scopes=true
+		}
+	}
+	if p.RedeemURL.String() == "" {
+		p.RedeemURL = &url.URL{Scheme: "https",
+			Host: "graph.facebook.com",
+			Path: "/v2.5/oauth/access_token",
+		}
+	}
+	if p.ProfileURL.String() == "" {
+		p.ProfileURL = &url.URL{Scheme: "https",
+			Host: "graph.facebook.com",
+			Path: "/v2.5/me",
+		}
+	}
+	if p.ValidateURL.String() == "" {
+		p.ValidateURL = p.ProfileURL
+	}
+	if p.Scope == "" {
+		p.Scope = "public_profile email"
+	}
+	return &FacebookProvider{ProviderData: p}
+}
+
+func getFacebookHeader(access_token string) http.Header {
+	header := make(http.Header)
+	header.Set("Accept", "application/json")
+	header.Set("x-li-format", "json")
+	header.Set("Authorization", fmt.Sprintf("Bearer %s", access_token))
+	return header
+}
+
+func (p *FacebookProvider) GetEmailAddress(s *SessionState) (string, error) {
+	if s.AccessToken == "" {
+		return "", errors.New("missing access token")
+	}
+	req, err := http.NewRequest("GET", p.ProfileURL.String()+"?fields=name,email", nil)
+	if err != nil {
+		return "", err
+	}
+	req.Header = getFacebookHeader(s.AccessToken)
+
+	type result struct {
+		Email string
+	}
+	var r result
+	err = api.RequestJson(req, &r)
+	if err != nil {
+		return "", err
+	}
+	if r.Email == "" {
+		return "", errors.New("no email")
+	}
+	return r.Email, nil
+}
+
+func (p *FacebookProvider) ValidateSessionState(s *SessionState) bool {
+	return validateToken(p, s.AccessToken, getFacebookHeader(s.AccessToken))
+}

providers/providers.go

@@ -22,6 +22,8 @@ func New(provider string, p *ProviderData) Provider {
 		return NewMyUsaProvider(p)
 	case "linkedin":
 		return NewLinkedInProvider(p)
+	case "facebook":
+		return NewFacebookProvider(p)
 	case "github":
 		return NewGitHubProvider(p)
 	case "azure":