Your Django project maybe required to hosted under a shared domain, but use a separate subpath.
To make django generate right URLs and avoid cookie conflicts, do settings below:
FORCE_SCRIPT_NAME = '/A-site/'
CSRF_COOKIE_PATH = LANGUAGE_COOKIE_PATH = SESSION_COOKIE_PATH = FORCE_SCRIPT_NAME
LOGIN_URL = '{0}api-auth/login/'.format(FORCE_SCRIPT_NAME)
LOGOUT_URL = '{0}api-auth/logout/'.format(FORCE_SCRIPT_NAME)
SPECTACULAR_SETTINGS["SERVERS"] = [{"url": FORCE_SCRIPT_NAME}] # work with drf-spectacular
References: