feat: Add browser-only connections to Enterprise (#4135)

* feat: Add browser-only connections to Enterprise

Fixes #4131.

* Fix formatting

coderd/coderd.go

@@ -489,8 +489,9 @@ func New(options *Options) *API {
 
 type API struct {
 	*Options
-	Auditor  atomic.Pointer[audit.Auditor]
-	HTTPAuth *HTTPAuthorizer
+	Auditor                           atomic.Pointer[audit.Auditor]
+	WorkspaceClientCoordinateOverride atomic.Pointer[func(rw http.ResponseWriter) bool]
+	HTTPAuth                          *HTTPAuthorizer
 
 	// APIHandler serves "/api/v2"
 	APIHandler chi.Router

coderd/workspaceagents.go

@@ -403,6 +403,11 @@ func (api *API) workspaceAgentClientCoordinate(rw http.ResponseWriter, r *http.R
 		httpapi.ResourceNotFound(rw)
 		return
 	}
+	// This is used by Enterprise code to control the functionality of this route.
+	override := api.WorkspaceClientCoordinateOverride.Load()
+	if override != nil && (*override)(rw) {
+		return
+	}
 
 	api.websocketWaitMutex.Lock()
 	api.websocketWaitGroup.Add(1)