### gapi.auth2.init Parameters Example

Source: https://developers.google.com/identity/sign-in/web/reference

Example of parameters for initializing the GoogleAuth object with a client ID.

```json
{
  client_id: 'CLIENT_ID.apps.googleusercontent.com'
}

```

--------------------------------

### gapi.signin2.render Options Example

Source: https://developers.google.com/identity/sign-in/web/reference

An example of the options object used to configure the sign-in button rendered by `gapi.signin2.render`.

```javascript
{
  scope: 'email',
  width: 200,
  height: 50,
  longtitle: true,
  theme: 'dark',
  onsuccess: handleSuccess,
  onfailure: handleFailure
}
```

--------------------------------

### Run PHP Built-in Web Server

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Start the PHP built-in web server to host your OAuth 2.0 example application. This command binds the server to localhost on port 8080.

```bash
php -S localhost:8080 ~/php-oauth2-example
```

--------------------------------

### gapi.auth2.authorize Configuration Example

Source: https://developers.google.com/identity/sign-in/web/reference

An example of the parameters object used for one-time OAuth 2.0 authorization with `gapi.auth2.authorize`.

```javascript
{
  client_id: 'CLIENT_ID.apps.googleusercontent.com',
  scope: 'email profile openid',
  response_type: 'id_token permission'
}
```

--------------------------------

### Install Dependencies with CocoaPods

Source: https://developers.google.com/identity-toolkit/v3

After modifying the Podfile, run this command to install the dependencies.

```bash
pod install
```

--------------------------------

### signIn(withPresentingWindow:hint:completion:)

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Starts an interactive sign-in flow on macOS using a provided window and an optional hint. This method is suitable for initiating sign-in when the app is not starting up.

```APIDOC
## signIn(withPresentingWindow:hint:completion:)

### Description
Starts an interactive sign-in flow on macOS using the provided hint. The completion block is called at the end of this process. Any saved sign-in state will be replaced by the result of this flow. This method should not be called when the app is starting up; use `restorePreviousSignInWithCompletion:` instead.

### Method
Objective-C

### Endpoint
N/A (SDK Method)

### Parameters
#### Path Parameters
N/A

#### Query Parameters
N/A

#### Request Body
N/A

### Request Example
Objective-C:
```objc
- (void)signInWithPresentingWindow:(id)presentingWindow
                              hint:(nullable NSString *)hint
                        completion:
                            (nullable void (^)(GIDSignInResult *_Nullable,
                                               NSError *_Nullable))completion;
```

Swift:
```swift
func signIn(withPresentingWindow presentingWindow: Any!, hint: String?) async throws -> GIDSignInResult
```

#### Parameters
* `_presentingWindow_` (Any!) - The window used to supply `presentationContextProvider` for `ASWebAuthenticationSession`.
* `_hint_` (NSString?) - An optional hint for the authorization server, for example the user’s ID or email address, to be prefilled if possible.
* `_completion_` (void (^)(GIDSignInResult *_Nullable, NSError *_Nullable)) - The optional block that is called on completion. This block will be called asynchronously on the main queue.

### Response
#### Success Response
- `GIDSignInResult` - The result of the sign-in operation.

#### Response Example
N/A (Completion block handles results)
```

--------------------------------

### Install Node.js Google Auth Library

Source: https://developers.google.com/identity/gsi/web/guides/verify-google-id-token

Install the Google Auth Library for Node.js using npm. This library is required to verify ID tokens.

```bash
npm install google-auth-library --save
```

--------------------------------

### Start Interactive Sign-In with Hint (macOS)

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Starts an interactive sign-in flow on macOS with an optional hint for the authorization server. This method should not be called during app startup.

```objc
- (void)signInWithPresentingWindow:(id)presentingWindow
                              hint:(nullable NSString *)hint
                        completion:
                            (nullable void (^)(GIDSignInResult *_Nullable,
                                               NSError *_Nullable))completion;
```

--------------------------------

### Install Google Auth Library for Ruby

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Install the Google Auth Library for Ruby using the gem command. This library is required for authentication with Google APIs.

```bash
gem install googleauth
```

--------------------------------

### Install Firebase SDK

Source: https://developers.google.com/identity/toolkit/migrate-firebase

After adding the Firebase pod to your Podfile, run 'pod install' to integrate the SDK into your Xcode project.

```bash
pod install

```

--------------------------------

### Install Google API Client Library for Python

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Use pip to install the Google APIs Client Library for Python. Ensure you are using Python 3.7 or greater.

```bash
pip install --upgrade google-api-python-client
```

--------------------------------

### Install Google APIs Client Libraries for Ruby

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Install the client libraries for Google Drive and Calendar APIs for Ruby using gem. These libraries provide access to specific Google services.

```bash
gem install google-apis-drive_v3 google-apis-calendar_v3
```

--------------------------------

### Install PHP Google API Client Library

Source: https://developers.google.com/identity/gsi/web/guides/verify-google-id-token

Install the Google API Client Library for PHP using Composer. This library is needed to verify ID tokens in PHP applications.

```bash
composer require google/apiclient
```

--------------------------------

### Install Sinatra for Ruby Web Applications

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Install the Sinatra web application framework for Ruby using gem. Sinatra is a lightweight framework often used for building web applications.

```bash
gem install sinatra
```

--------------------------------

### Start Interactive Sign-In with Hint and Scopes (macOS)

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Starts an interactive sign-in flow on macOS, accepting a hint and an array of additional scopes. This method is intended for use when the app is not initializing.

```objc
- (void)signInWithPresentingWindow:(id)presentingWindow
                              hint:(nullable NSString *)hint
                  additionalScopes:
                      (nullable NSArray<NSString *> *)additionalScopes
                        completion:
                            (nullable void (^)(GIDSignInResult *_Nullable,
                                               NSError *_Nullable))completion;
```

--------------------------------

### Example GET Request with Authorization Code

Source: https://developers.google.com/identity/oauth2/web/guides/use-code-model

This is an example of a GET request to an authorization endpoint, including URL parameters like state, code, scope, and user information. Clients must ignore unrecognized parameters.

```http
Request URL: https://www.example.com/auth-code?state=42a7bd822fe32cc56&code=4/0AX4XfWiAvnXLqxlckFUVao8j0zvZUJ06AMgr-n0vSPotHWcn9p-zHCjqwr47KHS_vDvu8w&scope=email%20profile%20https://www.googleapis.com/auth/calendar.readonly%20https://www.googleapis.com/auth/photoslibrary.readonly%20https://www.googleapis.com/auth/contacts.readonly%20openid%20https://www.googleapis.com/auth/userinfo.email%20https://www.googleapis.com/auth/userinfo.profile&authuser=0&hd=example.com&prompt=consent

```

--------------------------------

### Create Project Directory

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Create a new directory for your OAuth 2.0 example and navigate into it. This is a prerequisite for setting up the project.

```bash
mkdir ~/php-oauth2-example
cd ~/php-oauth2-example
```

--------------------------------

### Userinfo Endpoint Request Example

Source: https://developers.google.com/identity/account-linking/oauth-linking

Example of an HTTP GET request to the userinfo endpoint, including the Authorization header with a Bearer token.

```http
GET /userinfo HTTP/1.1
Host: myservice.example.com
Authorization: Bearer ACCESS_TOKEN


```

--------------------------------

### Google Sign-In Initialization and Listener Setup

Source: https://developers.google.com/identity/sign-in/web/listeners

Initializes the Google Sign-In v2 library and sets up listeners for sign-in state and user changes. This code should be called after the gapi library is loaded.

```javascript
var auth2;
var googleUser;

/**
 * Calls startAuth after Sign in V2 finishes setting up.
 */
var appStart = function() {
  gapi.load('auth2', initSigninV2);
};

/**
 * Initializes Signin v2 and sets up listeners.
 */
var initSigninV2 = function() {
  auth2 = gapi.auth2.init({
      client_id: 'CLIENT_ID.apps.googleusercontent.com',
      scope: 'profile'
  });

  // Listen for sign-in state changes.
  auth2.isSignedIn.listen(signinChanged);

  // Listen for changes to current user.
  auth2.currentUser.listen(userChanged);

  // Sign in the user if they are currently signed in.
  if (auth2.isSignedIn.get() == true) {
    auth2.signIn();
  }

  // Start with the current live values.
  refreshValues();
};

/**
 * Listener method for sign-out live value.
 *
 * @param {boolean} val the updated signed out state.
 */
var signinChanged = function (val) {
  console.log('Signin state changed to ', val);
  document.getElementById('signed-in-cell').innerText = val;
};

/**
 * Listener method for when the user changes.
 *
 * @param {GoogleUser} user the updated user.
 */
var userChanged = function (user) {
  console.log('User now: ', user);
  googleUser = user;
  updateGoogleUser();
  document.getElementById('curr-user-cell').innerText =
    JSON.stringify(user, undefined, 2);
};

/**
 * Updates the properties in the Google User table using the current user.
 */
var updateGoogleUser = function () {
  if (googleUser) {
    document.getElementById('user-id').innerText = googleUser.getId();
    document.getElementById('user-scopes').innerText =
      googleUser.getGrantedScopes();
    document.getElementById('auth-response').innerText =
      JSON.stringify(googleUser.getAuthResponse(), undefined, 2);
  } else {
    document.getElementById('user-id').innerText = '--';
    document.getElementById('user-scopes').innerText = '--';
    document.getElementById('auth-response').innerText = '--';
  }
};

/**
 * Retrieves the current user and signed in states from the GoogleAuth
 * object.
 */
var refreshValues = function() {
  if (auth2){
    console.log('Refreshing values...');

    googleUser = auth2.currentUser.get();

    document.getElementById('curr-user-cell').innerText =
      JSON.stringify(googleUser, undefined, 2);
    document.getElementById('signed-in-cell').innerText =
      auth2.isSignedIn.get();

    updateGoogleUser();
  }
}
```

--------------------------------

### Start SMS Retriever Client

Source: https://developers.google.com/identity/sms-retriever/request

Get an instance of SmsRetrieverClient and start listening for a matching SMS message. The retriever waits for one SMS message for up to 5 minutes.

```java
SmsRetrieverClient client = SmsRetriever.getClient(this /* context */);

Task<Void> task = client.startSmsRetriever();

task.addOnSuccessListener(new OnSuccessListener<Void>() {
  @Override
  public void onSuccess(Void aVoid) {
    // Successfully started retriever, expect broadcast intent
    // ...
  }
});

task.addOnFailureListener(new OnFailureListener() {
  @Override
  public void onFailure(@NonNull Exception e) {
    // Failed to start retriever, inspect Exception for more details
    // ...
  }
});
```

--------------------------------

### OAuth 2.0 Web Server Flow Example in Python (Flask)

Source: https://developers.google.com/identity/protocols/oauth2/web-server

This Python Flask application demonstrates the complete OAuth 2.0 web server flow, including user authorization, token exchange, and making authenticated API calls. Ensure you have Flask and Requests installed (`pip install Flask requests`).

```python
import json
import flask
import requests

app = flask.Flask(__name__)

# To get these credentials (CLIENT_ID CLIENT_SECRET) and for your application, visit
# https://console.cloud.google.com/apis/credentials.
CLIENT_ID = '123456789.apps.googleusercontent.com'
CLIENT_SECRET = 'abc123'  # Read from a file or environmental variable in a real app

# Access scopes for two non-Sign-In scopes: Read-only Drive activity and Google Calendar.
SCOPE = 'https://www.googleapis.com/auth/drive.metadata.readonly https://www.googleapis.com/auth/calendar.readonly'

# Indicate where the API server will redirect the user after the user completes
# the authorization flow. The redirect URI is required. The value must exactly
# match one of the authorized redirect URIs for the OAuth 2.0 client, which you
# configured in the API Console. If this value doesn't match an authorized URI,
# you will get a 'redirect_uri_mismatch' error.
REDIRECT_URI = 'http://example.com/oauth2callback'

@app.route('/')
def index():
  if 'credentials' not in flask.session:
    return flask.redirect(flask.url_for('oauth2callback'))

  credentials = json.loads(flask.session['credentials'])

  if credentials['expires_in'] <= 0:
    return flask.redirect(flask.url_for('oauth2callback'))
  else: 
    # User authorized the request. Now, check which scopes were granted.
    if 'https://www.googleapis.com/auth/drive.metadata.readonly' in credentials['scope']:
      # User authorized read-only Drive activity permission.
      # Example of using Google Drive API to list filenames in user's Drive.
      headers = {'Authorization': 'Bearer {}'.format(credentials['access_token'])}
      req_uri = 'https://www.googleapis.com/drive/v2/files'
      r = requests.get(req_uri, headers=headers).text
    else:
      # User didn't authorize read-only Drive activity permission.
      # Update UX and application accordingly
      r = 'User did not authorize Drive permission.'

    # Check if user authorized Calendar read permission.
    if 'https://www.googleapis.com/auth/calendar.readonly' in credentials['scope']:
      # User authorized Calendar read permission.
      # Calling the APIs, etc.
      r += 'User authorized Calendar permission.'
    else:
      # User didn't authorize Calendar read permission.
      # Update UX and application accordingly
      r += 'User did not authorize Calendar permission.'

  return r

@app.route('/oauth2callback')
def oauth2callback():
  if 'code' not in flask.request.args:
    state = str(uuid.uuid4())
    flask.session['state'] = state
    # Generate a url that asks permissions for the Drive activity
    # and Google Calendar scope. Then, redirect user to the url.
    auth_uri = ('https://accounts.google.com/o/oauth2/v2/auth?response_type=code'
                '&client_id={}&redirect_uri={}&scope={}&state={}').format(CLIENT_ID, REDIRECT_URI,
                                                                          SCOPE, state)
    return flask.redirect(auth_uri)
  else:
    if 'state' not in flask.request.args or flask.request.args['state'] != flask.session['state']:
      return 'State mismatch. Possible CSRF attack.', 400

    auth_code = flask.request.args.get('code')
    data = {'code': auth_code,
            'client_id': CLIENT_ID,
            'client_secret': CLIENT_SECRET,
            'redirect_uri': REDIRECT_URI,
            'grant_type': 'authorization_code'}

    # Exchange authorization code for access and refresh tokens (if access_type is offline)
    r = requests.post('https://oauth2.googleapis.com/token', data=data)
    flask.session['credentials'] = r.text
    return flask.redirect(flask.url_for('index'))

if __name__ == '__main__':
  import uuid
  app.secret_key = str(uuid.uuid4())
  app.debug = False
  app.run()

```

--------------------------------

### Initialize Google Sign-In and App Check

Source: https://developers.google.com/identity/sign-in/ios/appcheck/get-started

In your app delegate's `didFinishLaunchingWithOptions` method, call `GIDSignIn.sharedInstance.configure` for production or `GIDSignIn.sharedInstance.configureDebugProvider` for testing. This should be called early in the app lifecycle.

```swift
import SwiftUI
import GoogleSignIn

class AppDelegate: NSObject, UIApplicationDelegate {
  func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil
  ) -> Bool {
    #if targetEnvironment(simulator)
    // Configure for debugging.
    // See: https://developers.google.com/identity/sign-in/ios/appcheck/debug-provider
    #else
    GIDSignIn.sharedInstance.configure { error in
      if let error {
        print("Error configuring `GIDSignIn` for Firebase App Check: \(error)")
      }
    }
    #endif

    return true
  }
}

@main
struct YourAppNameApp: App {
  @UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate

  // ...
}

```

--------------------------------

### HTTP GET Request using Authorization Header

Source: https://developers.google.com/identity/protocols/oauth2/native-app

Example of calling the Drive Files API using the 'Authorization: Bearer' HTTP header. This method is preferred over query string parameters.

```http
GET /drive/v2/files HTTP/1.1
Host: www.googleapis.com
Authorization: Bearer access_token
```

--------------------------------

### Sign In with Presenting Window and Hint

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Initiates the Google sign-in flow with a hint, using a presenting window.

```APIDOC
## -signInWithPresentingWindow:hint:completion:

### Description
Initiates the Google sign-in flow with an optional hint, presenting the sign-in UI modally using a window.

### Method
Instance Method

### Endpoint
N/A (Instance Method)

### Parameters
- **presentingWindow** (UIWindow) - The window that will present the sign-in UI.
- **hint** (NSString) - An optional hint for the sign-in process (e.g., user's email).
- **completion** (GIDSignInCallback) - A block that is executed upon completion of the sign-in operation. It receives a GIDGoogleUser object and an error if one occurred.

### Response
None
```

--------------------------------

### Get Auth Token using Chrome Identity API

Source: https://developers.google.com/identity/protocols/oauth2/resources/oob-migration

Retrieve an access token for a Chrome App client using the Chrome Identity API. This example demonstrates interactive token retrieval.

```javascript
window.onload = function() {
  document.querySelector('button').addEventListener('click', function() {

  **
  // retrieve access token
  chrome.identity.getAuthToken({interactive: true}, function(token) {
  **
  // ..........


  // the example below shows how to use a retrieved access token with an appropriate scope
  // to call the Google People API contactGroups.get endpoint

  fetch(
    'https://people.googleapis.com/v1/contactGroups/all?maxMembers=20&key=API_KEY',
    init)
    .then((response) => response.json())
    .then(function(data) {
      console.log(data)
    });
   });
 });
};
```

--------------------------------

### Configure One Tap Prompt Login Hint

Source: https://developers.google.com/identity/gsi/web/guides/handle-credential-responses-js-functions

Provide a login hint for the One Tap prompt using HTML attributes. This example sets the login hint to 'user@example.com'.

```html
<div class="g_id_signin" data-login_hint="user@example.com"></div>
```

--------------------------------

### API Call with Signed JWT Bearer Token

Source: https://developers.google.com/identity/protocols/oauth2/service-account

Example of an HTTP GET request to a Google API using a signed JWT as the Authorization bearer token. Ensure the 'Authorization' header is correctly formatted.

```http
GET /v1/projects/abc/databases/123/indexes HTTP/1.1
Authorization: Bearer SIGNED_JWT
Host: firestore.googleapis.com
```

--------------------------------

### Initialize and Prompt with Google Accounts

Source: https://developers.google.com/identity/gsi/web/reference/js-reference

Implement the `onGoogleLibraryLoad` callback to initialize Google accounts and prompt the user. This code should be placed within a script tag.

```html
<script>
  window.onGoogleLibraryLoad = () => {
   google.accounts.id.initialize({
     ...
   });
   google.accounts.id.prompt();
  };
</script>
```

--------------------------------

### Sign In with Presenting View Controller and Hint

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Initiates the Google sign-in flow with a hint, using a presenting view controller.

```APIDOC
## -signInWithPresentingViewController:hint:completion:

### Description
Initiates the Google sign-in flow with an optional hint, presenting the sign-in UI modally.

### Method
Instance Method

### Endpoint
N/A (Instance Method)

### Parameters
- **presentingViewController** (UIViewController) - The view controller that will present the sign-in UI.
- **hint** (NSString) - An optional hint for the sign-in process (e.g., user's email).
- **completion** (GIDSignInCallback) - A block that is executed upon completion of the sign-in operation. It receives a GIDGoogleUser object and an error if one occurred.

### Response
None
```

--------------------------------

### Get Auth Token and Call Google People API (Chrome App)

Source: https://developers.google.com/identity/protocols/oauth2/resources/loopback-migration

Retrieve an access token using chrome.identity.getAuthToken and use it to call the Google People API's contactGroups.get endpoint. This example demonstrates accessing contacts without a loopback IP address redirect URI.

```javascript
window.onload = function() {
  document.querySelector('button').addEventListener('click', function() {

  // retrieve access token
  chrome.identity.getAuthToken({interactive: true}, function(token) {
  

  // the example below shows how to use a retrieved access token with an appropriate scope
  // to call the Google People API contactGroups.get endpoint

  fetch(
    'https://people.googleapis.com/v1/contactGroups/all?maxMembers=20&key=API_KEY',
    init)
    .then((response) => response.json())
    .then(function(data) {
      console.log(data)
    });
   });
 });
};
```

--------------------------------

### Create and Launch Hint Request

Source: https://developers.google.com/identity/smartlock-passwords/android/retrieve-hints

Configure a HintRequest to prompt the user to choose an email address. Pass this request to getHintPickerIntent and then start the intent sender.

```java
HintRequest hintRequest = new HintRequest.Builder()
        .setHintPickerConfig(new CredentialPickerConfig.Builder()
                .setShowCancelButton(true)
                .build())
        .setEmailAddressIdentifierSupported(true)
        .setAccountTypes(IdentityProviders.GOOGLE)
        .build();

PendingIntent intent = mCredentialsClient.getHintPickerIntent(hintRequest);
try {
    startIntentSenderForResult(intent.getIntentSender(), RC_HINT, null, 0, 0, 0);
} catch (IntentSender.SendIntentException e) {
    Log.e(TAG, "Could not start hint picker Intent", e);
}
```

--------------------------------

### Initialize GAPI and GIS with Token Model

Source: https://developers.google.com/identity/oauth2/web/guides/migration-to-gis

This HTML and JavaScript code demonstrates how to load both the GAPI client and the GIS token client, initialize them, and prepare for API calls. It uses Promises, async/await for managing library loading order and error handling.

```html
<!DOCTYPE html>
<html>
<head>
    <title>GAPI and GIS Example</title>
    <script async defer src="https://apis.google.com/js/api.js" onload="gapiLoad()"></script>
    <script async defer src="https://accounts.google.com/gsi/client" onload="gisLoad()"></script>
</head>
<body>
    <h1>GAPI Client with GIS Authorization</h1>
    <button id="authorizeBtn" style="visibility:hidden;">Authorize and Load Events</button>
    <button id="revokeBtn" style="visibility:hidden;">Revoke Access</button>
    <div id="content"></div>

    <script>
        const YOUR_CLIENT_ID = "YOUR_CLIENT_ID";
        const YOUR_API_KEY = 'YOUR_API_KEY';
        const CALENDAR_SCOPE = 'https://www.googleapis.com/auth/calendar.readonly';

        let tokenClient;
        let libsLoaded = 0;

        function gapiLoad() {
            gapi.load('client', initGapiClient);
        }

        async function initGapiClient() {
            try {
                await gapi.client.init({ apiKey: YOUR_API_KEY });
                await gapi.client.load('https://www.googleapis.com/discovery/v1/apis/calendar/v3/rest');
                console.log('GAPI client initialized.');
                checkAllLoaded();
            } catch (err) {
                handleError('GAPI initialization failed:', err);
            }
        }

        function gisLoad() {
            try {
                tokenClient = google.accounts.oauth2.initTokenClient({
                    client_id: YOUR_CLIENT_ID,
                    scope: CALENDAR_SCOPE,
                    callback: '', // Will be set dynamically
                    error_callback: handleGisError,
                });
                console.log('GIS TokenClient initialized.');
                checkAllLoaded();
            } catch (err) {
                handleError('GIS initialization failed:', err);
            }
        }

        function checkAllLoaded() {
            libsLoaded++;
            if (libsLoaded === 2) {
                document.getElementById('authorizeBtn').style.visibility = 'visible';
                document.getElementById('revokeBtn').style.visibility = 'visible';
                document.getElementById('authorizeBtn').onclick = makeApiCall;
                document.getElementById('revokeBtn').onclick = revokeAccess;
                console.log('Ready to authorize.');
            }
        }

        function handleGisError(err) {
            console.error('GIS Error:', err);
            let message = 'An error occurred during authorization.';
            if (err && err.type === 'popup_failed_to_open') {
                message = 'Failed to open popup. Please disable popup blockers.';
            } else if (err && err.type === 'popup_closed') {
                message = 'Authorization popup was closed.';
            }
            document.getElementById('content').textContent = message;
        }

        function handleError(message, error) {
            console.error(message, error);
            document.getElementById('content').textContent = `${message} ${error.message || JSON.stringify(error)}`;
        }

        async function makeApiCall() {
            document.getElementById('content').textContent = 'Processing...';
            try {
                let token = gapi.client.getToken();
                if (!token || !token.access_token) {
                    console.log('No token, fetching one...');
                    await getToken();
                }

```

--------------------------------

### Sign In with Presenting Window, Hint, and Additional Scopes

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Initiates the Google sign-in flow with a hint and additional scopes, using a presenting window.

```APIDOC
## -signInWithPresentingWindow:hint:additionalScopes:completion:

### Description
Initiates the Google sign-in flow with an optional hint and additional OAuth scopes, presenting the sign-in UI modally using a window.

### Method
Instance Method

### Endpoint
N/A (Instance Method)

### Parameters
- **presentingWindow** (UIWindow) - The window that will present the sign-in UI.
- **hint** (NSString) - An optional hint for the sign-in process (e.g., user's email).
- **additionalScopes** (NSArray<NSString>) - An array of additional OAuth scopes to request.
- **completion** (GIDSignInCallback) - A block that is executed upon completion of the sign-in operation. It receives a GIDGoogleUser object and an error if one occurred.

### Response
None
```

--------------------------------

### Initialize Podfile with CocoaPods

Source: https://developers.google.com/identity/sign-in/ios/start-integrating

Use this command to create a new Podfile in your project's root directory if one does not already exist.

```bash
pod init
```

--------------------------------

### Access Token Response Example

Source: https://developers.google.com/identity/protocols/oauth2/service-account

An example of a successful JSON response from the Authorization Server containing an access token.

```json
{
  "access_token": "1/8xbJqaOZXSUZbHLl5EOtu1pxz3fmmetKx9W8CV4t79M",
  "scope": "https://www.googleapis.com/auth/prediction"
  "token_type": "Bearer",
  "expires_in": 3600
}
```

--------------------------------

### Initialize Google Sign-In with Callback and Prompt

Source: https://developers.google.com/identity/gsi/web/reference/js-reference

Initializes the Google Sign-In client and prompts the user. This example includes an onload function to ensure initialization happens after the page loads.

```javascript
<script>
  window.onload = function () {
    google.accounts.id.initialize({
      client_id: 'YOUR_GOOGLE_CLIENT_ID',
      callback: handleCredentialResponse
    });
    google.accounts.id.prompt();
  };
</script>
```

--------------------------------

### Sign In with Presenting View Controller, Hint, and Additional Scopes

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDSignIn.html

Initiates the Google sign-in flow with a hint and additional scopes, using a presenting view controller.

```APIDOC
## -signInWithPresentingViewController:hint:additionalScopes:completion:

### Description
Initiates the Google sign-in flow with an optional hint and additional OAuth scopes, presenting the sign-in UI modally.

### Method
Instance Method

### Endpoint
N/A (Instance Method)

### Parameters
- **presentingViewController** (UIViewController) - The view controller that will present the sign-in UI.
- **hint** (NSString) - An optional hint for the sign-in process (e.g., user's email).
- **additionalScopes** (NSArray<NSString>) - An array of additional OAuth scopes to request.
- **completion** (GIDSignInCallback) - A block that is executed upon completion of the sign-in operation. It receives a GIDGoogleUser object and an error if one occurred.

### Response
None
```

--------------------------------

### Start Resolution for Credential Selection

Source: https://developers.google.com/identity/smartlock-passwords/android/retrieve-credentials

Call this method when a `ResolvableApiException` is caught to start the activity for the user to select a credential.

```Java
private void resolveResult(ResolvableApiException rae, int requestCode) {
    try {
        rae.startResolutionForResult(MainActivity.this, requestCode);
        mIsResolving = true;
    } catch (IntentSender.SendIntentException e) {
        Log.e(TAG, "Failed to send resolution.", e);
        hideProgress();
    }
}
```

--------------------------------

### OAuth 2.0 Authorization Code Response Example

Source: https://developers.google.com/identity/protocols/oauth2/web-server

This is an example of a successful authorization code response from the OAuth 2.0 server.

```url
https://oauth2.example.com/auth?code=4/P7q7W91a-oMsCeLvIaQm6bTrgtp7
```

--------------------------------

### OAuth 2.0 Error Response Example

Source: https://developers.google.com/identity/protocols/oauth2/web-server

This is an example of an error response from the OAuth 2.0 server, indicating that access was denied.

```url
https://oauth2.example.com/auth?error=access_denied
```

--------------------------------

### Example OAuth Error Response

Source: https://developers.google.com/identity/oauth2/web/guides/error

This is an example of an error response that OAuth may return. Your callback function will receive this response.

```json
{
  "error":"access_denied"
}
```

--------------------------------

### Open Swift Sample Project (Swift Package Manager)

Source: https://developers.google.com/identity/sign-in/ios/sample-app

Open the DaysUntilBirthday Swift sample project directly in Xcode when using Swift Package Manager. Dependencies will be added automatically.

```bash
open GoogleSignIn-iOS/Samples/Swift/DaysUntilBirthday/DaysUntilBirthday.xcodeproj
```

--------------------------------

### Install Google Authentication Libraries for Python

Source: https://developers.google.com/identity/protocols/oauth2/web-server

Install the necessary Google authentication libraries for Python using pip. These are required for user authorization.

```bash
pip install --upgrade google-auth google-auth-oauthlib google-auth-httplib2
```

--------------------------------

### GoogleAuth.signIn()

Source: https://developers.google.com/identity/sign-in/web/reference

Initiates the sign-in process for the user using the options previously configured with `gapi.auth2.init()`. Returns a Promise that resolves with the GoogleUser instance upon successful authentication or rejects with an error.

```APIDOC
## GoogleAuth.signIn()

### Description
Initiates the sign-in process for the user using the options previously configured with `gapi.auth2.init()`. Returns a Promise that resolves with the GoogleUser instance upon successful authentication or rejects with an error.

### Returns
- **Promise** - A `Promise` that is fulfilled with the `GoogleUser` instance when the user successfully authenticates and grants the requested scopes, or rejected with an object containing an `error` property if an error happened. See `GoogleAuth.signIn(options)` for error codes.
```

--------------------------------

### Error Response Example

Source: https://developers.google.com/identity/protocols/oauth2/javascript-implicit-flow

An example of an OAuth 2.0 error response, indicating that access was denied. This is returned on the hash fragment of the redirect URI.

```url
https://oauth2.example.com/callback#error=access_denied
```

--------------------------------

### gapi.auth2.authorize Usage Example

Source: https://developers.google.com/identity/sign-in/web/reference

Demonstrates how to perform a one-time OAuth 2.0 authorization and handle the response, including accessing tokens and using `gapi.client`.

```javascript
gapi.auth2.authorize({
  client_id: 'CLIENT_ID.apps.googleusercontent.com',
  scope: 'email profile openid',
  response_type: 'id_token permission'
}, function(response) {
  if (response.error) {
    // An error happened!
    return;
  }
  // The user authorized the application for the scopes requested.
  var accessToken = response.access_token;
  var idToken = response.id_token;
  // You can also now use gapi.client to perform authenticated requests.
});
```

--------------------------------

### Userinfo Endpoint Invalid Token Response Example

Source: https://developers.google.com/identity/account-linking/oauth-linking

Example of an HTTP 401 Unauthorized response from the userinfo endpoint when the access token is invalid.

```http
HTTP/1.1 401 Unauthorized
WWW-Authenticate: error="invalid_token",
error_description="The Access Token expired"


```

--------------------------------

### Initialize GIDConfiguration with all properties

Source: https://developers.google.com/identity/sign-in/ios/reference/Classes/GIDConfiguration.html

Initializes a GIDConfiguration object by specifying all available properties: client ID, server client ID, hosted domain, and OpenID realm.

```Swift
init(clientID: String, serverClientID: String?, hostedDomain: String?, openIDRealm: String?)
```

```Objective-C
- (nonnull instancetype)initWithClientID:(nonnull NSString *)clientID
                          serverClientID:(nullable NSString *)serverClientID
                            hostedDomain:(nullable NSString *)hostedDomain
                             openIDRealm:(nullable NSString *)openIDRealm;
```