Adds an authentication domain to this.
Each auth domain will have the chance to require authentication for each request that comes in; normally auth domains will require authentication for requests on certain paths that they have been set up to watch, or that meet other criteria set by the caller. If an auth domain determines that a request requires authentication (and the request doesn't contain authentication), this will automatically reject the request with an appropriate status (401 Unauthorized or 407 Proxy Authentication Required). If the request used the SoupServer:100-continue Expectation, this will reject it before the request body is sent.
| this |
a Server |
| auth_domain |