Make HTTP middleware easier to use

server/auth/xsrf/xsrf_test.go

Index: server/auth/xsrf/xsrf_test.go
diff --git a/server/auth/xsrf/xsrf_test.go b/server/auth/xsrf/xsrf_test.go
index fbda5788f4e6d1e68da6e44a757e93fa7999ee45..952872fbe7eb7a26bb2910fffde0fc07759c9748 100644
--- a/server/auth/xsrf/xsrf_test.go
+++ b/server/auth/xsrf/xsrf_test.go
@@ -17,6 +17,7 @@ import (
 	"golang.org/x/net/context"
 
 	"github.com/luci/luci-go/common/clock/testclock"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/secrets/testsecrets"
 
 	. "github.com/smartystreets/goconvey/convey"
@@ -42,26 +43,34 @@ func TestXsrf(t *testing.T) {
 		c := makeContext()
 		tok, _ := Token(c)
 
-		h := WithTokenCheck(func(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
-			rw.Write([]byte("hi"))
-		})
+		initialize := func(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) router.Handler {
+			return func(ctx *router.Context) {
+				ctx.Context = c
+				ctx.Writer = rw
+				ctx.Request = r
+				ctx.Params = p
+			}
+		}
+		handler := func(c *router.Context) {
+			c.Writer.Write([]byte("hi"))
+		}
 
 		// Has token -> works.
 		rec := httptest.NewRecorder()
 		req := makeRequest(tok)
-		h(c, rec, req, nil)
+		router.ChainHandlers(initialize(c, rec, req, nil), WithTokenCheck(), handler)()
 		So(rec.Code, ShouldEqual, 200)
 
 		// No token.
 		rec = httptest.NewRecorder()
 		req = makeRequest("")
-		h(c, rec, req, nil)
+		router.ChainHandlers(initialize(c, rec, req, nil), WithTokenCheck(), handler)()
 		So(rec.Code, ShouldEqual, 403)
 
 		// Bad token.
 		rec = httptest.NewRecorder()
 		req = makeRequest("blah")
-		h(c, rec, req, nil)
+		router.ChainHandlers(initialize(c, rec, req, nil), WithTokenCheck(), handler)()
 		So(rec.Code, ShouldEqual, 403)
 	})
 }