feat: Add Python User Authorization App sample

python/user-auth-app/.gcloudignore

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+# This file specifies files that are *not* uploaded to Google Cloud
+# using gcloud. It follows the same syntax as .gitignore, with the addition of
+# "#!include" directives (which insert the entries of the given .gitignore-style
+# file at that point).
+#
+# For more information, run:
+#   $ gcloud topic gcloudignore
+#
+.gcloudignore
+README.md
+# If you would like to upload your .git directory, .gitignore file or files
+# from your .gitignore file, remove the corresponding line
+# below:
+.git
+.gitignore

python/user-auth-app/.gitignore

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+client_secrets.json

python/user-auth-app/README.md

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+# Google Chat User Authorization App
+
+This sample demonstrates how to create a Google Chat app that requests
+authorization from the user to make calls to Chat API on their behalf. The first
+time the user interacts with the app, it requests offline OAuth tokens for the
+user and saves them to a Firestore database. If the user interacts with the app
+again, the saved tokens are used so the app can call Chat API on behalf of the
+user without asking for authorization again. Once saved, the OAuth tokens could
+even be used to call Chat API without the user being present.
+
+This app is built using Python on Google App Engine (Standard Environment) and
+leverages Google's OAuth2 for authorization and Firestore for data storage.
+
+**Key Features:**
+
+* **User Authorization:** Securely requests user consent to call Chat API with
+  their credentials.
+* **Chat API Integration:** Calls Chat API to post messages on behalf of the
+  user.
+* **Google Chat Integration:**  Responds to DMs or @mentions in Google Chat. If
+  necessary, request configuration to start an OAuth authorization flow.
+* **App Engine Deployment:**  Provides step-by-step instructions for deploying
+  to App Engine.
+* **Cloud Firestore:** Stores user tokens in a Firestore database.
+
+## Prerequisites
+
+* **Python 3:**  [Download](https://www.python.org/downloads/)
+* **Google Cloud SDK:**  [Install](https://cloud.google.com/sdk/docs/install)
+* **Google Cloud Project:**  [Create](https://console.cloud.google.com/projectcreate)
+
+##  Deployment Steps
+
+1. **Enable APIs:**
+
+   * Enable the Cloud Firestore and Google Chat APIs using the
+     [console](https://console.cloud.google.com/apis/enableflow?apiid=firestore.googleapis.com,chat.googleapis.com)
+     or gcloud:
+
+     ```bash
+     gcloud services enable firestore.googleapis.com chat.googleapis.com
+     ```
+
+1. **Initiate Deployment to App Engine:**
+
+   * Go to [App Engine](https://console.cloud.google.com/appengine) and
+     initialize an application.
+
+   * Deploy the User Authorization app to App Engine:
+
+     ```bash
+     gcloud app deploy
+     ```
+
+1. **Create and Use OAuth Client ID:**
+
+   * Get the app hostname:
+
+     ```bash
+     gcloud app describe | grep defaultHostname
+     ```
+
+   * In your Google Cloud project, go to
+     [APIs & Services > Credentials](https://console.cloud.google.com/apis/credentials).
+   * Click `Create Credentials > OAuth client ID`.
+   * Select `Web application` as the application type.
+   * Add `<hostname from the previous step>/oauth2` to `Authorized redirect URIs`.
+   * Download the JSON file and rename it to `client_secrets.json` in your
+     project directory.
+   * Redeploy the app with the file `client_secrets.json`:
+
+     ```bash
+     gcloud app deploy
+     ```
+
+1. **Create a Firestore Database:**
+
+   *  Create a Firestore database in native mode named `auth-data` using the
+      [console](https://console.cloud.google.com/firestore) or gcloud:
+
+      ```bash
+      gcloud firestore databases create \
+      --database=auth-data \
+      --location=REGION \
+      --type=firestore-native
+      ```
+
+      Replace `REGION` with a
+      [Firestore location](https://cloud.google.com/firestore/docs/locations#types)
+      such as `nam5` or `eur3`.
+
+## Create the Google Chat app
+
+* Go to
+  [Google Chat API](https://console.cloud.google.com/apis/api/chat.googleapis.com/hangouts-chat)
+  and click `Configuration`.
+* In **App name**, enter `User Auth App`.
+* In **Avatar URL**, enter `https://developers.google.com/chat/images/quickstart-app-avatar.png`.
+* In **Description**, enter `Quickstart app`.
+* Under Functionality, select **Receive 1:1 messages** and
+  **Join spaces and group conversations**.
+* Under **Connection settings**, select **HTTP endpoint URL** and enter your App
+  Engine app's URL (obtained in the previous deployment steps).
+* In **Authentication Audience**, select **HTTP endpoint URL**.
+* Under **Visibility**, select **Make this Google Chat app available to specific
+  people and groups in your domain** and enter your email address.
+* Click **Save**.
+
+The Chat app is ready to receive and respond to messages on Chat.
+
+## Interact with the App
+
+* Add the app to a Google Chat space.
+* @mention the app.
+* Follow the authorization link to grant the app access to your account.
+* Once authorization is complete, the app will post a message to the space using
+  your credentials.
+* If you @mention the app again, it will post a new message to the space with
+  your credentials using the saved tokens, without asking for authorization again.
+
+## Related Topics
+
+* [Authenticate and authorize as a Google Chat user](https://developers.google.com/workspace/chat/authenticate-authorize-chat-user)
+* [Receive and respond to user interactions](https://developers.google.com/workspace/chat/receive-respond-interactions)

python/user-auth-app/app.yaml

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+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+runtime: python312

python/user-auth-app/firestore_service.py

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+# Copyright 2025 Google LLC. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an 'AS IS' BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Functions to handle database operations."""
+
+from google.cloud import firestore
+
+# The prefix used by the Google Chat API in the User resource name.
+USERS_PREFIX = "users/"
+
+# The name of the users collection in the database.
+USERS_COLLECTION = "users"
+
+# Initialize the Firestore database using Application Default Credentials.
+db = firestore.Client(database="auth-data")
+
+def store_token(user_name: str, access_token: str, refresh_token: str):
+    """Saves the user's OAuth2 tokens to storage."""
+    doc_ref = db.collection(USERS_COLLECTION).document(user_name.replace(USERS_PREFIX, ""))
+    doc_ref.set({ "accessToken": access_token, "refreshToken": refresh_token })
+
+def get_token(user_name: str) -> dict | None:
+    """Fetches the user's OAuth2 tokens from storage."""
+    doc = db.collection(USERS_COLLECTION).document(user_name.replace(USERS_PREFIX, "")).get()
+    if doc.exists:
+        return doc.to_dict()
+    return None

python/user-auth-app/main.py

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+# Copyright 2025 Google LLC. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an 'AS IS' BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""The main script for the project, which starts a Flask app
+to listen to HTTP requests from Chat events and the OAuth flow callback."""
+
+import logging
+import os
+import flask
+from werkzeug.middleware.proxy_fix import ProxyFix
+from request_verifier import verify_google_chat_request
+from oauth_flow import oauth2callback
+from user_auth_post import post_with_user_credentials
+
+logging.basicConfig(
+    level=logging.INFO,
+    style="{",
+    format="[{levelname:.1}{asctime} {filename}:{lineno}] {message}"
+)
+
+app = flask.Flask(__name__)
+app.wsgi_app = ProxyFix(app.wsgi_app)
+
+@app.route("/", methods=["GET"])
+def on_get() -> dict:
+    """App route that handles unsupported GET requests."""
+    return "Hello! This endpoint is meant to be called from Google Chat."
+
+@app.route("/", methods=["POST"])
+def on_event() -> dict:
+    """App route that responds to interaction events from Google Chat."""
+    if not verify_google_chat_request(flask.request):
+        return "Hello! This endpoint is meant to be called from Google Chat."
+    if event := flask.request.get_json(silent=True):
+        if event["message"]:
+            # Post a message back to the same Chat space using user credentials.
+            return flask.jsonify(post_with_user_credentials(event))
+        # Ignore events that don't contain a message.
+        return flask.jsonify({})
+    return "Error: Unknown action"
+
+@app.route("/oauth2", methods=["GET"])
+def on_oauth2():
+    """App route that handles callback requests from the OAuth2 authorization flow.
+    The handler exhanges the code received from the OAuth2 server with a set of
+    credentials, stores the authentication and refresh tokens in the database,
+    and redirects the request to the config complete URL provided in the request.
+    """
+    return oauth2callback(flask.request.url)
+
+if __name__ == "__main__":
+    PORT=os.getenv("PORT", "8080")
+    app.run(port=PORT)

python/user-auth-app/oauth_flow.py

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+# Copyright 2025 Google LLC. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an 'AS IS' BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Functions to handle the OAuth authentication flow."""
+
+import json
+import logging
+from urllib.parse import parse_qs, urlparse
+
+import flask
+import google_auth_oauthlib.flow
+from google.auth.transport import requests
+from google.oauth2 import id_token
+from google.oauth2.credentials import Credentials
+from firestore_service import store_token
+
+# This variable specifies the name of a file that contains the OAuth 2.0
+# information for this application, including its client_id and client_secret.
+CLIENT_SECRETS_FILE = "client_secrets.json"
+
+# Application OAuth credentials.
+KEYS = json.load(open(CLIENT_SECRETS_FILE, encoding="UTF-8"))["web"]
+
+# Define the app's authorization scopes.
+# Note: 'openid' is required to that Google Auth will return a JWT with the
+# user id, which we can use to validate that the user who granted consent is
+# the same who requested it (to avoid identity theft).
+SCOPES = ["openid", "https://www.googleapis.com/auth/chat.messages.create"]
+
+def generate_auth_url(user_name: str, config_complete_redirect_url: str) -> str:
+    """Generates the URL to start the OAuth2 authorization flow."""
+    flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(
+        CLIENT_SECRETS_FILE, scopes=SCOPES)
+    flow.redirect_uri = KEYS["redirect_uris"][0]
+    # Generate URL for request to Google's OAuth 2.0 server.
+    auth_url, _ = flow.authorization_url(
+        # Enable offline access so that you can refresh an access token without
+        # re-prompting the user for permission.
+        access_type="offline",
+        # Optional, enable incremental authorization. Recommended as a best practice.
+        include_granted_scopes="true",
+        state=json.dumps({
+            "userName": user_name,
+            "configCompleteRedirectUrl": config_complete_redirect_url
+        })
+    )
+    return auth_url
+
+def create_credentials(access_token: str, refresh_token: str) -> Credentials:
+    """Returns the Credentials to authenticate using the user tokens."""
+    return Credentials(
+        token = access_token,
+        refresh_token = refresh_token,
+        token_uri = KEYS["token_uri"],
+        client_id = KEYS["client_id"],
+        client_secret = KEYS["client_secret"],
+        scopes = SCOPES
+    )
+
+def oauth2callback(url: str):
+    """Handles an OAuth2 callback request.
+    If the authorization was succesful, it exchanges the received code with the
+    access and refresh tokens and saves them into Firestore to be used when
+    calling the Chat API. Then, it redirects the response to the
+    configCompleteRedirectUrl specified in the authorization URL.
+    If the authorization fails, it just prints an error message to the response.
+    """
+    flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(
+        CLIENT_SECRETS_FILE, scopes=SCOPES)
+    flow.redirect_uri = KEYS["redirect_uris"][0]
+
+    # Fetch state from url
+    parsed = urlparse(url)
+    qs = parse_qs(parsed.query)
+    if "error" in qs:
+        # An error response e.g. error=access_denied.
+        logging.warning("Error: %s", qs["error"][0])
+        return "Error: " + qs["error"][0]
+
+    # Use the authorization server's response to fetch the OAuth 2.0 tokens.
+    if "code" not in qs:
+        logging.warning("Error: invalid query code.")
+        return "Error: invalid query code."
+    code = qs["code"][0]
+    flow.fetch_token(code=code)
+    credentials = flow.credentials
+    token = id_token.verify_oauth2_token(
+        credentials.id_token, requests.Request(), KEYS["client_id"])
+    user_name = "users/" + token["sub"]
+
+    # Save tokens to the database so the app can use them to make API calls.
+    store_token(user_name, credentials.token, credentials.refresh_token)
+
+    # Validate that the user who granted consent is the same who requested it.
+    if "state" not in qs:
+        logging.warning("Error: invalid query state.")
+        return "Error: invalid query state."
+    state = json.loads(qs["state"][0])
+    if user_name != state["userName"]:
+        logging.warning("Error: token user does not correspond to request user.")
+        return """Error: the user who granted consent does not correspond to
+            the user who initiated the request. Please start the configuration
+            again and use the same account you're using in Google Chat."""
+
+    # Redirect to the URL that tells Google Chat that the configuration is
+    # completed.
+    return flask.redirect(state["configCompleteRedirectUrl"])