Master GOOGLE SIGNIN with FastAPI Tutorial

In this tutorial, we will learn how to implement Google Signin in FastAPI like a pro. Google Signin is a popular way for users to log in to your web application using their Google account. By implementing Google Signin in your FastAPI application, you can provide a convenient and secure way for users to log in without having to remember yet another password.

To implement Google Signin in FastAPI, we will use the OAuth 2.0 protocol. This allows our application to securely interact with Google’s servers to authenticate users and obtain their profile information. We will also use the Google Signin API to facilitate the login process.

Before we begin, make sure you have the following prerequisites:

1. Python installed on your machine
2. FastAPI installed on your machine
3. A Google Developer account with a project set up
4. The necessary OAuth client ID and client secret from your Google Developer account

Now, let’s get started with the implementation:

Step 1: Create a FastAPI application

First, create a new FastAPI application by running the following command in your terminal:

$ pip install fastapi uvicorn
$ mkdir fastapi-google-signin
$ cd fastapi-google-signin
$ touch main.py

Next, open the main.py file in your text editor and add the following code:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def read_root():
    return {"Hello": "World"}

This code simply creates a basic FastAPI application with a single endpoint that returns a simple JSON response.

Step 2: Set up Google Signin credentials

Next, log in to your Google Developer account and create a new project if you haven’t already. Navigate to the "Credentials" section of your project and create a new OAuth 2.0 client ID. Select "Web application" as the application type and enter the appropriate redirect URI for your FastAPI application (e.g., http://localhost:8000/auth/google/callback).

Make note of the client ID and client secret generated for your OAuth client. You will need these later to authenticate with Google’s servers.

Step 3: Implement Google Signin endpoint

Now, let’s implement the endpoint that handles the Google Signin flow in our FastAPI application. Add the following code to your main.py file:

from fastapi import FastAPI, HTTPException
from fastapi.responses import RedirectResponse

app = FastAPI()

@app.get("/auth/google")
async def google_signin():
    return RedirectResponse(f"https://accounts.google.com/o/oauth2/v2/auth?response_type=code&client_id=YOUR_CLIENT_ID&redirect_uri=http://localhost:8000/auth/google/callback&scope=openid%20profile%20email&access_type=offline")

Replace YOUR_CLIENT_ID with the OAuth client ID you obtained from your Google Developer account earlier.

This code sets up a GET endpoint /auth/google that redirects the user to Google’s OAuth 2.0 authentication endpoint with the necessary parameters. The user will be prompted to log in to their Google account and grant permission to your application to access their profile information.

Step 4: Handle Google Signin callback

Next, we need to set up the callback endpoint that handles the response from Google’s servers once the user has authenticated. Add the following code to your main.py file:

from fastapi import FastAPI, HTTPException
from fastapi.responses import RedirectResponse

app = FastAPI()

@app.get("/auth/google/callback")
async def google_signin_callback(code: str):
    # Exchange authorization code for access token
    # Verify access token and obtain user information
    return {"message": "Google Signin successful"}

This code sets up a GET endpoint /auth/google/callback that expects a query parameter code containing the authorization code returned by Google’s servers. In this callback function, you will need to exchange this authorization code for an access token and verify the token to obtain the user’s profile information. This is typically done by making a POST request to Google’s token endpoint.

Step 5: Run your FastAPI application

Finally, you can run your FastAPI application by running the following command in your terminal:

$ uvicorn main:app --reload

This will start your FastAPI application on http://localhost:8000. You can now navigate to http://localhost:8000/auth/google in your browser to initiate the Google Signin flow.

Congratulations! You have successfully implemented Google Signin in your FastAPI application like a pro. You can now customize the authentication flow, store user information in a database, and provide a seamless user experience on your web application. Happy coding!