Add Webfinger endpoint (#19462)

This adds the [Webfinger](https://webfinger.net/) endpoint for federation.

Supported schemes are `acct` and `mailto`. The profile and avatar url are returned as metadata.

routers/web/web.go

@@ -282,6 +282,13 @@ func RegisterRoutes(m *web.Route) {
 		}
 	}
 
+	federationEnabled := func(ctx *context.Context) {
+		if !setting.Federation.Enabled {
+			ctx.Error(http.StatusNotFound)
+			return
+		}
+	}
+
 	// FIXME: not all routes need go through same middleware.
 	// Especially some AJAX requests, we can reduce middleware number to improve performance.
 	// Routers.
@@ -289,9 +296,10 @@ func RegisterRoutes(m *web.Route) {
 	m.Get("/", Home)
 	m.Group("/.well-known", func() {
 		m.Get("/openid-configuration", auth.OIDCWellKnown)
-		if setting.Federation.Enabled {
+		m.Group("", func() {
 			m.Get("/nodeinfo", NodeInfoLinks)
-		}
+			m.Get("/webfinger", WebfingerQuery)
+		}, federationEnabled)
 		m.Get("/change-password", func(w http.ResponseWriter, req *http.Request) {
 			http.Redirect(w, req, "/user/settings/account", http.StatusTemporaryRedirect)
 		})