added google auth api contract (#202)

Author: byt3quester

auth/README.md

@@ -0,0 +1,100 @@
+# Auth
+
+## Endpoints
+
+| Route | Method | Description |
+|-------|--------|-------------|
+| [/auth/google/login](#get-authgooglelogin) | GET | Initiates the Google OAuth authentication |
+| [/auth/google/callback](#get-authgooglecallback) | GET | Handles the callback from Google after the user authenticates |
+
+## GET /auth/google/login
+
+Initiates the Google OAuth authentication process by redirecting the user to Google's consent screen.
+
+- **Params**
+  None
+
+- **Query**
+  - Optional: `redirectURL=[string]` (The URL to redirect the user to after authentication is successful. It should be a valid URL.)
+
+### Response
+
+- **Success Response**:
+  - **Code:** 302  
+
+  - **Content:** Redirects to Google's OAuth 2.0 consent screen for user authentication.
+
+    ```text
+    Location: https://accounts.google.com/o/oauth2/v2/auth?client_id={CLIENT_ID}&redirect_uri={REDIRECT_URI}&response_type=code&scope=email&state={redirectURL}
+    ```
+
+- **Error Response:**
+  - **Code:** 401
+  - **Content:**
+
+    ```json
+    { 
+      "statusCode": 401, 
+      "error": "Unauthorized", 
+      "message": "User cannot be authenticated" 
+    }
+    ```
+  - **Code:** 500
+
+  - **Content:**
+
+    ```json
+    {
+      "statusCode": 500,
+      "error": "Internal Server Error",
+      "message": "An internal server error occurred"
+    }
+    ```
+
+## GET /auth/google/callback
+
+Handles the callback from Google after the user authenticates, exchanges the authorization code for an access token, and completes the user login process.
+
+- **Params**
+  None
+
+- **Query**
+  - Required: `code=[string]` (The authorization code returned by Google after the user grants consent.)
+  - Required: `state=[string]` (The state parameter returned by Google, used to verify the request’s legitimacy and ensure security.)
+
+### Response
+
+- **Success Response**:
+  - **Code**: 302
+  - **Content**: Redirects to the specified redirectURL or https://my.realdevsquad.com/new-signup if user details are incomplete.
+
+    ```
+    Location: {redirectURL}
+    ```
+  - **Cookie**: A secure JWT authentication token (rds-session) is set as a cookie to maintain the user's session.
+    ```
+    Set-Cookie: rds-session=<jwt_token>; Domain={realdevsqual.com}; Expires={expirationTime}; HttpOnly; Secure; SameSite=Lax
+    ```
+
+- **Error Response:**
+  - **Code:** 401
+  - **Content:**
+
+    ```json
+    { 
+      "statusCode": 401, 
+      "error": "Unauthorized", 
+      "message": "User cannot be authenticated" 
+    }
+    ```
+  - **Code:** 500
+
+  - **Content:**
+
+    ```json
+    {
+      "statusCode": 500,
+      "error": "Internal Server Error",
+      "message": "An internal server error occurred"
+    }
+    ```