python - Apache的WSGI模块链接postgresql数据库的用户权限问题

在Udacity上学习Linux Web Server课程的时候最后一道实践题上卡住了，题目是这样的：

Exercise
Update your /var/www/html/myapp.wsgi application so that it successfully connects to your database, queries a table for data and presents that piece of data rather than the text Hello World!. You will need to create a table and populate it with data of your choosing, then query it from your app.

数据库，数据表已经建好，在命令行用python以postgres用户身份也能链接成功。但是同样的代码写到wsgi文件里之后却无法链接成功。我想问题还是出在访问权限上，如何让wsgi模块能有权限访问数据库呢？