[Fixed]-How safe is a solution of writing/reading secret file from within Django app?

You might keep in mind that changing the SECRET_KEY setting via that max_age variable might have some consequences that impact your app. This SO question discusses some of the ways that the SECRET_KEY is used with Django.

Effects of changing Django's SECRET_KEY

You might check to make sure that you are not using your app in such a way that changing that setting would impact you.