In the C driver, there are setters for URI options. For example, we can use a function like mongoc_uri_set_auth_source to set the URI's auth source.

There's no such concept in the C++ driver. Instead, users are forced to pass options through the URI string. This is error-prone; a typo in a string will throw a runtime error at best, while a typo in a function name will cause a compile-time error.