FIX: Memory Leak and Security Risk with Static Token Buffer (#264)

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[AB#37606](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/37606)

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### Summary   
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This pull request improves the handling of sensitive data when setting
SQL connection attributes in `connection.cpp`. The main change is
replacing a static buffer with a stack-allocated buffer to better
control memory and securely erase sensitive data after use.

Sensitive data handling:

* Replaced the static vector of buffers with a stack-allocated
`std::string` (`buffer`) to temporarily hold sensitive data when setting
SQL attributes. This avoids unnecessary retention of sensitive data in
memory.
* Added logic to zero out the contents of `buffer` after it is used,
ensuring sensitive data does not remain in memory.
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Author: gargsaumya

mssql_python/pybind/connection/connection.cpp

@@ -173,16 +173,16 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
     LOG("Setting SQL attribute");
     SQLPOINTER ptr = nullptr;
     SQLINTEGER length = 0;
+    std::string buffer; // to hold sensitive data temporarily
 
     if (py::isinstance<py::int_>(value)) {
         int intValue = value.cast<int>();
         ptr = reinterpret_cast<SQLPOINTER>(static_cast<uintptr_t>(intValue));
         length = SQL_IS_INTEGER;
     } else if (py::isinstance<py::bytes>(value) || py::isinstance<py::bytearray>(value)) {
-        static std::vector<std::string> buffers;
-        buffers.emplace_back(value.cast<std::string>());
-        ptr = const_cast<char*>(buffers.back().c_str());
-        length = static_cast<SQLINTEGER>(buffers.back().size());
+        buffer = value.cast<std::string>();  // stack buffer
+        ptr = buffer.data();
+        length = static_cast<SQLINTEGER>(buffer.size());
     } else {
         LOG("Unsupported attribute value type");
         return SQL_ERROR;
@@ -195,6 +195,11 @@ SQLRETURN Connection::setAttribute(SQLINTEGER attribute, py::object value) {
     else {
         LOG("Set attribute successfully");
     }
+    
+    // Zero out sensitive data if used
+    if (!buffer.empty()) {
+        std::fill(buffer.begin(), buffer.end(), static_cast<char>(0));
+    }
     return ret;
 }