Add example OAuth workflow

Author: youmikoh

README.md

@@ -70,6 +70,8 @@ pip install --upgrade ShopifyAPI
     # you should save the access token now for future use.
     ```
 
+    > See an [example OAuth workflow here](docs/oauth-workflow-example.md)
+
 1.  Now you're ready to make authorized API requests to your shop!:
 
     ```python

docs/oauth-workflow-example.md

@@ -0,0 +1,58 @@
+# Example OAuth workflow
+
+The Shopify Python API [validates HMAC and timing attacks](https://shopify.dev/apps/auth/oauth/getting-started#step-2-verify-the-installation-request) with the `request_token` function. Below is a basic example OAuth workflow for a FastAPI app. 
+
+
+## Setup
+
+1. Create a new application in the Partners Dashboard, and retrieve your API key and API secret.
+
+2. Configure your app URL and Admin API version. Initialize your `shopify.Session` class with your API key and API secret for authentication.
+
+```python
+import shopify
+
+VERSION = "2022-07"
+HOST = "https://app-url"
+
+API_KEY = "api-key"
+API_SECRET = "api-secret"
+
+shopify.Session.setup(api_key=API_KEY, secret=API_SECRET)
+``` 
+
+3. Request permissions from the merchant with the `auth_url` from the `create_permission_url` function. Once the merchant acccepts, a temporary token `code` is sent to the specified `redirect_uri` of your app.
+
+```python
+from fastapi import FastAPI, Request
+from fastapi.responses import RedirectResponse
+
+@app.get("/", response_class=RedirectResponse)
+async def install(shop_name: str):
+    shop_url = f"{shop_name}.myshopify.com"
+    state = binascii.b2a_hex(os.urandom(15)).decode("utf-8")
+    redirect_uri = f"{HOST}/auth/shopify/callback"
+    scopes = ['read_products']
+
+    new_session = shopify.Session(shop_url, VERSION)
+    auth_url = new_session.create_permission_url(scopes, redirect_uri, state)
+    return RedirectResponse(
+        url=auth_url, 
+        status_code=303
+    )
+```
+
+4. To capture the `code`, set up a callback handler in your app. To exchange the temporary token for a permanent access token, supply the parameters from this request to the `request_token` function. 
+
+```python
+@app.get("/auth/shopify/callback")
+async def auth_callback(request: Request):
+    request_params = dict(request.query_params)
+    shop_url = request_params.get("shop")
+    
+    session = shopify.Session(shop_url, VERSION)
+    access_token = session.request_token(request_params)
+    # store access_token
+```
+
+