Refactor token handling and introduce token revocation logic

Updated `decode_token` for stricter validation of token claims and explicit error handling. Added utilities for token revocation and verification, improving

backend/tests/auth/dependencies.py

@@ -1,3 +1,4 @@
+from datetime import datetime, timezone
 from unittest.mock import AsyncMock
 
 import pytest
@@ -21,13 +22,22 @@ def mock_user():
 
 @pytest.mark.asyncio
 async def test_get_current_user_success(mock_user):
-    valid_token = jwt.encode({"sub": str(mock_user.id), "type": "access"}, SECRET_KEY, algorithm=ALGORITHM)
+    # Create a valid access token with required claims
+    valid_token = jwt.encode(
+        {"sub": str(mock_user.id), "type": "access", "exp": datetime.now(tz=timezone.utc).timestamp() + 3600},
+        SECRET_KEY,
+        algorithm=ALGORITHM
+    )
 
+    # Mock database session
     mock_db = AsyncMock()
-    mock_db.get.return_value = mock_user
+    mock_db.get.return_value = mock_user  # Ensure `db.get()` returns the mock_user
 
+    # Call the dependency
     user = await get_current_user(token=valid_token, db=mock_db)
-    assert user == mock_user
+
+    # Assertions
+    assert user == mock_user, "Returned user does not match the mocked user."
     mock_db.get.assert_called_once_with(User, mock_user.id)