Chrome overrides User-Agent specified as parameter

Q&A (please complete the following information)

• OS: macOS
• Browser: chrome
• Browser Version: 70.0.3538.77
• Method of installation: dist assets
• Swagger-UI version: 3.19.5
• Swagger/OpenAPI version: Swagger 2.0

Content & configuration

Example Swagger/OpenAPI definition:

      - name: "User-Agent"
        in: "header"
        description: "user agent"
        required: true
        type: "string"
        default: "CustomAgent"

Swagger-UI configuration options:

    window.onload = function() {
      // Begin Swagger UI call region
      const ui = SwaggerUIBundle({
        url: "swagger.yaml",
        dom_id: '#swagger-ui',
        deepLinking: true,
        presets: [
          SwaggerUIBundle.presets.apis,
          SwaggerUIStandalonePreset
        ],
        plugins: [
          SwaggerUIBundle.plugins.DownloadUrl
        ],
        layout: "StandaloneLayout"
      })
      // End Swagger UI call region

      window.ui = ui
    }

Describe the bug you're encountering

Browser always overrides User-Agent header and sends its own, no matter what value I type into parameter

To reproduce...

Steps to reproduce the behavior:

1. Go to method with User-Agent parameter
2. Click on Execute

Expected behavior

Request is sent with User-Agent equal to specified parameter

Actual behavior

Request is sent with standard browser User-Agent

Reproduce the issue in Chrome using the supplied Swagger 2.0 definition and Swagger UI configuration, then inspect the request generated after clicking Execute. Trace the request execution path to determine where the entered User-Agent value is handled, and verify the result against the stated expected and actual behavior.