Risk Level: high
Platform: OpenAPI
Spectral Rule ID: OPENAPI001

REMEDIATION

Define securityDefinitions and ensure it is not empty.

swagger: '2.0'
info:
  version: 1.0.0
  title: Sample API
+ securityDefinitions:
+   api_key:
+     type: apiKey
+     name: api_key
+     in: header
paths:
  /users:
    get:
      security:
        - api_key: []
      responses:
        '200':
          description: A list of users.

# OR

openapi: 3.0.0
info:
  version: 1.0.0
  title: Sample API
+ components:
+   securitySchemes:
+     app_id:
+       .
+       .
+       .
paths:
  /users:
    get:
      summary: List all users
+     security:
+       - app_id: []
      responses:
        '200':
          description: A list of users.
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/User'

Read more:

https://swagger.io/docs/specification/2-0/authentication/