feat: add setup for temp users

Add setup for alternative signin credentials for temp users and a
function check_auth to handle both these and the permanent credentials.

To setup a temp user for the app, their username and password should be
set in environment variables TEMP_USERNAME and TEMP_PASSWORD and the
expiry of their access should be set in TEMP_EXPIRY_TIME_SG_ISO_8601,
in Singapore time and ISO 8601 format.

app.py

@@ -8,6 +8,8 @@ import json # For conversion of OpenAI responses into json/dictionary objects so
 from dotenv import load_dotenv # For loading environment variables in local environment
 from collections import Counter # For tabulating tag occurrences
 import logging
+import time
+from datetime import datetime
 
 logger = logging.getLogger()
 logger.setLevel(logging.INFO)
@@ -169,6 +171,31 @@ def process_quotes(quotes_file_path: str, quotes_col_name: str, tags_string: str
         tags_counter_df.to_excel(writer, sheet_name='Tag Count', index=False)
     logger.info('Results written to Excel')
     return output_df, tags_counter_df, output_file_path
+
+def check_auth(username:str, password:str):
+    """
+    Authenticate the user.
+    
+    Verifies the user's credentials against the values stored in the environment variables.
+    User may authenticate with permanent username and password(for TFT team) or temporary username and password.
+    For temporary username and password, they will only be valid before the expiry time as set in the environment variables.
+
+    Returns True or False depending on authentication success.
+    """
+    # Check permanent credentials
+    if username == os.getenv('APP_USERNAME') and password == os.getenv('APP_PASSWORD'):
+        return True
+
+    # Check temporary credentials
+    if (
+        username == os.getenv('TEMP_USERNAME') and 
+        password == os.getenv('TEMP_PASSWORD') and 
+        time.time() < datetime.fromisoformat(os.getenv('TEMP_EXPIRY_TIME_SG_ISO_8601').replace("Z", "+08:00")).timestamp()
+    ):
+        return True
+
+    # Invalid credentials
+    return False
     
 # Define user interface structure
 demo = gr.Interface(
@@ -188,4 +215,4 @@ demo = gr.Interface(
     description=INSTRUCTIONS 
     )
 
-demo.launch(share=True, auth=(os.getenv('APP_USERNAME'), os.getenv('APP_PASSWORD')), ssr_mode=False)
+demo.launch(share=True, auth=check_auth, ssr_mode=False)