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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

While using the Cloud Endpoints service from Google Cloud, I notice that the document query builder on @nestjs/swagger did not support the following feature of CE: https://docs.cloud.google.com/endpoints/docs/openapi/oasv3-extensions?#x-google-endpoint

servers:
  - url: https://API_NAME.apigateway.PROJECT_ID.cloud.goog/v1
    x-google-endpoint: {}

because we can't add custom fields to the servers[*] entry -- the x-google-endpoint, for example.

There is a way to circumvent that limitation but it looks hacky.

What is the new behavior?

The .addServer now supports a new parameter dedicated for custom attributes for each entry in the servers field of OpenAPI v3. Note that I'm not a fan of having 4 parameters but this was the only way to avoid breaking changes - we could improve that in the next major version.

.addServer("https://API_NAME.apigateway.PROJECT_ID.cloud.goog/v1", "Cloud Endpoints service URL", undefined, {
  'x-google-endpoint': {
    allowCors: true,
   },
   'foo-bar': {},
})

will output the following:

servers:
  - url: https://API_NAME.apigateway.PROJECT_ID.cloud.goog/v1
    description: Cloud Endpoints service URL
    x-google-endpoint:
      allowCors: true
    foo-bar: {}

Does this PR introduce a breaking change?

• Yes
• No