enable facebook login

app/auth/__init__.py

@@ -8,4 +8,5 @@ from .views import (
     forgot_password,
     github,
     google,
+    facebook,
 )

app/auth/templates/auth/login.html

@@ -84,6 +84,11 @@
              class="btn btn-block btn-social btn-google">
             <i class="fa fa-google"></i> Sign in with Google
           </a>
+
+          <a href="{{ url_for('auth.facebook_login', next=next_url) }}"
+             class="btn btn-block btn-social btn-facebook">
+            <i class="fa fa-facebook"></i> Sign in with Facebook
+          </a>
         </div>
       </div>
 

app/auth/templates/auth/register.html

@@ -73,6 +73,12 @@
              class="btn btn-block btn-social btn-google">
             <i class="fa fa-google"></i> Sign up with Google
           </a>
+
+          <a href="{{ url_for('auth.facebook_login', next=next_url) }}"
+             class="btn btn-block btn-social btn-facebook">
+            <i class="fa fa-facebook"></i> Sign up with Facebook
+          </a>
+
         </div>
       </div>
     </div>

app/auth/views/facebook.py

@@ -0,0 +1,127 @@
+import arrow
+from flask import request, session, redirect, url_for, flash
+from flask_login import login_user
+from requests_oauthlib import OAuth2Session
+from requests_oauthlib.compliance_fixes import facebook_compliance_fix
+
+from app.auth.base import auth_bp
+from app.auth.views.google import create_file_from_url
+from app.config import URL, FACEBOOK_CLIENT_ID, FACEBOOK_CLIENT_SECRET
+from app.email_utils import notify_admin
+from app.extensions import db
+from app.log import LOG
+from app.models import User
+from app.utils import random_string
+
+_authorization_base_url = "https://www.facebook.com/dialog/oauth"
+_token_url = "https://graph.facebook.com/oauth/access_token"
+
+_scope = ["email"]
+
+# need to set explicitly redirect_uri instead of leaving the lib to pre-fill redirect_uri
+# when served behind nginx, the redirect_uri is localhost... and not the real url
+_redirect_uri = URL + "/auth/facebook/callback"
+
+
+@auth_bp.route("/facebook/login")
+def facebook_login():
+    # to avoid flask-login displaying the login error message
+    session.pop("_flashes", None)
+
+    next_url = request.args.get("next")
+
+    # Facebook does not allow to append param to redirect_uri
+    # we need to pass the next url by session
+    if next_url:
+        session["facebook_next_url"] = next_url
+
+    facebook = OAuth2Session(
+        FACEBOOK_CLIENT_ID, scope=_scope, redirect_uri=_redirect_uri
+    )
+    facebook = facebook_compliance_fix(facebook)
+    authorization_url, state = facebook.authorization_url(_authorization_base_url)
+
+    # State is used to prevent CSRF, keep this for later.
+    session["oauth_state"] = state
+    return redirect(authorization_url)
+
+
+@auth_bp.route("/facebook/callback")
+def facebook_callback():
+    facebook = OAuth2Session(
+        FACEBOOK_CLIENT_ID,
+        state=session["oauth_state"],
+        scope=_scope,
+        redirect_uri=_redirect_uri,
+    )
+    facebook = facebook_compliance_fix(facebook)
+    token = facebook.fetch_token(
+        _token_url,
+        client_secret=FACEBOOK_CLIENT_SECRET,
+        authorization_response=request.url,
+    )
+
+    # Fetch a protected resource, i.e. user profile
+    # {
+    #     "email": "abcd@gmail.com",
+    #     "id": "1234",
+    #     "name": "First Last",
+    #     "picture": {
+    #         "data": {
+    #             "url": "long_url"
+    #         }
+    #     }
+    # }
+    facebook_user_data = facebook.get(
+        "https://graph.facebook.com/me?fields=id,name,email,picture{url}"
+    ).json()
+
+    email = facebook_user_data["email"]
+    user = User.get_by(email=email)
+
+    picture_url = facebook_user_data.get("picture", {}).get("data", {}).get("url")
+
+    if user:
+        if picture_url and not user.profile_picture_id:
+            LOG.d("set user profile picture to %s", picture_url)
+            file = create_file_from_url(picture_url)
+            user.profile_picture_id = file.id
+            db.session.commit()
+
+        login_user(user)
+    # create user
+    else:
+        LOG.d("create facebook user with %s", facebook_user_data)
+        user = User.create(email=email, name=facebook_user_data["name"])
+
+        # set a random password
+        user.set_password(random_string(20))
+
+        user.activated = True
+
+        if picture_url:
+            LOG.d("set user profile picture to %s", picture_url)
+            file = create_file_from_url(picture_url)
+            user.profile_picture_id = file.id
+
+        db.session.commit()
+        login_user(user)
+
+        flash(f"Welcome to SimpleLogin {user.name}!", "success")
+
+        notify_admin(
+            f"new user signs up {user.email}", f"{user.name} signs up at {arrow.now()}"
+        )
+
+    # The activation link contains the original page, for ex authorize page
+    if "facebook_next_url" in session:
+        next_url = session["facebook_next_url"]
+        LOG.debug("redirect user to %s", next_url)
+
+        # reset the next_url to avoid user getting redirected at each login :)
+        session.pop("facebook_next_url", None)
+
+        return redirect(next_url)
+    else:
+        LOG.debug("redirect user to dashboard")
+        return redirect(url_for("dashboard.index"))