Provide MockWebServer Integration

I'd like Spring Boot to provide integration with MockWebServer. For my particular case, I'd like to be able to leverage MockWebServer.url to configure environment variables for testing. For example, a user of Spring Boot's Security OAuth2 support might want to provide a value for spring.security.oauth2.resourceserver.jwt.issuer-uri that points to the MockWebServer.

One way a user might be able to integrate this is by providing a property that looks like:

spring.security.oauth2.resourceserver.jwt.issuer-uri=${mockwebserver.url}/oauth2/keys

Spring Boot could provide a hook that would change ${mockwebserver.url} into a URL created using MockWebServer.url.

A few points of consideration:

• The MockWebServer will need to be accessible to the user to add mock responses
• We need to be able to reset the MockWebServer between tests.
• User's may want to customize the MockWebServer

Start by reviewing the requested MockWebServer integration and the example spring.security.oauth2.resourceserver.jwt.issuer-uri property. Determine how users would access, reset, and customize MockWebServer instances and how the ${mockwebserver.url} placeholder should be resolved. Done means these integration points are defined and the OAuth2 testing example works.