当在 Adonis Js 中遇到授权失败的问题时，可以按照以下步骤进行解决：

1. 确保已经安装了 Adonis Js 的授权包 @adonisjs/shield，可以通过以下命令进行安装：

npm install @adonisjs/shield

2. 在 start/app.js 文件中添加以下代码来加载授权中间件：

const { shield } = require('@adonisjs/shield')

const providers = [
  // ...
  '@adonisjs/shield/providers/ShieldProvider'
]

const aceProviders = [
  // ...
  '@adonisjs/shield/providers/ShieldProvider'
]

const middleware = [
  // ...
  'Adonis/Middleware/Shield'
]

3. 在 middleware.js 文件中添加以下代码，以定义授权规则：

'use strict'

const Config = use('Config')

module.exports = {
  /*
  |--------------------------------------------------------------------------
  | Default Auth Guard
  |--------------------------------------------------------------------------
  |
  | The default auth guard used during authentication. The same can be
  | defined inside `config/auth.js` file.
  |
  */
  // auth: 'web',

  /*
  |--------------------------------------------------------------------------
  | Default Gate
  |--------------------------------------------------------------------------
  |
  | The default gate defines the namespace and the driver for resolving
  | policies. It works out of the box without any configuration.
  |
  */
  // gate: 'Adonis/Can/Gate',

  /*
  |--------------------------------------------------------------------------
  | Default Shield Policy
  |--------------------------------------------------------------------------
  |
  | A default shield policy is required by the shield middleware to handle
  | the authorization. The policy can be a closure or a reference to a
  | class. Though using a class is the recommended way.
  |
  */
  shield: {
    // policy: 'Adonis/Can/Policy',
    policy: async (ctx, next, args) => {
      // Define your authorization logic here
      await next()
    }
  }
}

4. 在需要授权的路由中使用 auth:shield 中间件来进行授权：

Route.get('/protected-route', () => {
  // Add your protected route logic here
}).middleware(['auth:shield'])

通过以上步骤，可以解决 Adonis Js 授权失败的问题。根据你的实际需求，在 shield.policy 中定义授权逻辑，以确保只有经过授权的用户可以访问受保护的路由。