title: Specify options available on API endpoint for a path variable with Swagger in Spring Boot
body: <p>I have the following controller method</p>
  
  <pre><code>@ApiOperation(value = "Send a signin request with a provider")
  @GetMapping("/{provider}/signin")
  public void signIn(@PathVariable String provider, HttpServletResponse response) {
      service.signIn(provider, response);
  }
  </code></pre>
  
  <p>And what I want to know is if there is <strong>way to specify the possible values</strong>, that can be passed in the <strong>provider path variable</strong>. 
  On the Swagger docs I see something about enums, but I don't know how to use this on my Spring Boot app. 
  And on the SpringFox docs I couldn't find the word enum.
  Thanks in advance</p>