Environment Variables in definition

Sorry if this came up before, I searched but could not find anything.

Environment variables have become something of the de facto mechanism to set server-specific values, then access them from software. The hosting providers I have worked with (AWS, Heroku, OpenShift) all offer features to easily set/import/export them and most software I've seen meant to run on these systems uses it for things like environment specific URLs, secrets etc.

But afaik there is no way to reference environment variables in an OpenAPI definition.

Would this be a feature to support? I imagine the definition having a section (probably at the top level) that specified a set of environment variables expected to be set, and possibly the default values to use when they are not set. Those variables could then be used in other parts of the definition.

My practical use cases comes from needing to set different authorization urls for different environments. Currently I am rendering swagger.json from JSP to implement this myself, but it seems to me this is a very generic use case that many people will face.

See also e.g.
https://github.com/OAI/OpenAPI-Specification/issues/169
https://github.com/OAI/OpenAPI-Specification/issues/779
https://github.com/swagger-api/swagger-ui/pull/3410

No implementation files or tests are named. Start by reading the discussion, the linked OpenAPI issues, and the Swagger UI pull request to understand the intended scope. Done requires an agreed, implementable environment-variable model for definitions, including how values are declared and referenced.