Make HTTP middleware easier to use

server/auth/xsrf/xsrf.go

Index: server/auth/xsrf/xsrf.go
diff --git a/server/auth/xsrf/xsrf.go b/server/auth/xsrf/xsrf.go
index 7fa964a9668c2d975fef651c8a6eeddf880f6d8e..c5fd847f57ab7d496591a025f7d0135da228404d 100644
--- a/server/auth/xsrf/xsrf.go
+++ b/server/auth/xsrf/xsrf.go
@@ -16,14 +16,13 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/julienschmidt/httprouter"
 	"golang.org/x/net/context"
 
 	"github.com/luci/luci-go/common/errors"
 	"github.com/luci/luci-go/common/logging"
 
 	"github.com/luci/luci-go/server/auth"
-	"github.com/luci/luci-go/server/middleware"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/tokens"
 )
 
@@ -70,21 +69,19 @@ func TokenField(c context.Context) template.HTML {
 // If searches for the token in "xsrf_token" POST form field (as generated by
 // TokenField). Aborts the request with HTTP 403 if XSRF token is missing or
 // invalid.
-func WithTokenCheck(h middleware.Handler) middleware.Handler {
-	return func(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
-		tok := r.PostFormValue("xsrf_token")
-		if tok == "" {
-			replyError(c, rw, http.StatusForbidden, "XSRF token is missing")
-			return
-		}
-		switch err := Check(c, tok); {
-		case errors.IsTransient(err):
-			replyError(c, rw, http.StatusInternalServerError, "Transient error when checking XSRF token - %s", err)
-		case err != nil:
-			replyError(c, rw, http.StatusForbidden, "Bad XSRF token - %s", err)
-		default:
-			h(c, rw, r, p)
-		}
+func WithTokenCheck(c *router.Context, next router.Handler) {
+	tok := c.Request.PostFormValue("xsrf_token")
+	if tok == "" {
+		replyError(c.Context, c.Writer, http.StatusForbidden, "XSRF token is missing")
+		return
+	}
+	switch err := Check(c.Context, tok); {
+	case errors.IsTransient(err):
+		replyError(c.Context, c.Writer, http.StatusInternalServerError, "Transient error when checking XSRF token - %s", err)
+	case err != nil:
+		replyError(c.Context, c.Writer, http.StatusForbidden, "Bad XSRF token - %s", err)
+	default:
+		next(c)
 	}
 }