Update OAuth2.md

OAuth2.md

@@ -1,3 +1,12 @@
+OAuth2 Flow:
+
+1. User clicks "Login with Google" on your platform (xorismesiti.gr).
+2. Authorization Request: Redirect to Google's authorization endpoint, requesting the user's profile and email.
+3. User Login and Consent: User logs in to Google and grants permissions.
+4. Authorization Code Response: Google redirects back to your platform with an authorization code.
+5. Access Token Request: Exchange the authorization code for an access token.
+6. Access Protected Resources: Use the access token to fetch the user's Google profile and email.
+7. Token Refresh (Optional): If the token expires, use the refresh token to get a new access token.
 
 # 1. Authorization Request (User Initiates Login)
 
@@ -137,3 +146,40 @@ Authorization: Bearer ya29.a0AfH6SMC8Op6zXZkHi2XITkDoOVzYXt3hTY6sny54UlWlxrnKlX5
 ```
 
 
+# 7. Refreshing the Access Token (If Necessary)
+
+If the access token expires, 
+
+your platform can use the refresh token (if provided) to obtain a new access token without requiring the user to log in again.
+
+- `URL`: https://oauth2.googleapis.com/token
+- `HTTP` Method: POST
+- `Headers`:
+- `Content`-Type: application/x-www-form-urlencoded
+- `Body` Parameters:
+- `grant_type`=refresh_token: This indicates the refresh token flow.
+- `refresh_token`: The refresh token obtained in step 5.
+- `client_id`: Your Google API client ID.
+- `client_secret`: Your Google API client secret.
+
+**Request**
+
+```sh
+POST https://oauth2.googleapis.com/token
+Content-Type: application/x-www-form-urlencoded
+
+grant_type=refresh_token&
+refresh_token=1//04d5XHqmn6Hdy3wTf5OYDP1SyBa74zEFURjddQ2A1cFw78PY13pQyWhlD2A6XhDQtKlrjAqU4kS3vGdMvckw&
+client_id=YOUR_GOOGLE_CLIENT_ID&
+client_secret=YOUR_GOOGLE_CLIENT_SECRET
+``
+
+**Response**
+
+```json
+{
+    "access_token": "ya29.a0AfH6SMC8Op6zXZkHi2XITkDoOVzYXt3hTY6sny54UlWlxrnKlX5Xv78is7BEHekVX-VoA",
+    "token_type": "Bearer",
+    "expires_in": 3600
+}
+```