Get "app" instance in middleware

[foubei]

What happens?

Unable to get the app instance in middlewares

Mini Showcase Repository(REQUIRED)

Provide a mini GitHub repository which can reproduce the issue.
Use npm init egg --type=simple bug then upload to your GitHub

How To Reproduce

Steps to reproduce the behavior:

1. I am unable to put the authentication code inside middleware instead of controller. the app.passport is inaccessible in middleware.

Expected behavior

1. Able to access app.passport directly from middleware and handle the authentication

Context

• Node Version: 10.19.0
• Egg Version: 2.15.1
• Plugin Name: egg-passport
• Plugin Version: 2.1.1
• Platform: Ubuntu

[egg-bot]

Hello @foubei. Please provide a reproducible example following the instruction.

Issues labeled by Need Reproduce will be closed if no activities in 7 days.

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@foubei，请根据这个说明提供最小可复现代码。

如果在 7 天内没有进展会被自动关闭。