1 files changed, 171 insertions, 0 deletions
diff --git a/services/context/csrf.go b/services/context/csrf.go
new file mode 100644
index 0000000..e0518a4
--- /dev/null
+++ b/services/context/csrf.go
@@ -0,0 +1,171 @@
+// Copyright 2013 Martini Authors
+// Copyright 2014 The Macaron Authors
+// Copyright 2021 The Gitea Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License"): you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations
+// under the License.
+// SPDX-License-Identifier: Apache-2.0
+
+// a middleware that generates and validates CSRF tokens.
+
+package context
+
+import (
+	"html/template"
+	"net/http"
+	"strconv"
+	"time"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
+)
+
+const (
+	CsrfHeaderName  = "X-Csrf-Token"
+	CsrfFormName    = "_csrf"
+	CsrfErrorString = "Invalid CSRF token."
+)
+
+// CSRFProtector represents a CSRF protector and is used to get the current token and validate the token.
+type CSRFProtector interface {
+	// PrepareForSessionUser prepares the csrf protector for the current session user.
+	PrepareForSessionUser(ctx *Context)
+	// Validate validates the csrf token in http context.
+	Validate(ctx *Context)
+	// DeleteCookie deletes the csrf cookie
+	DeleteCookie(ctx *Context)
+}
+
+type csrfProtector struct {
+	opt CsrfOptions
+	// id must be unique per user.
+	id string
+	// token is the valid one which wil be used by end user and passed via header, cookie, or hidden form value.
+	token string
+}
+
+// CsrfOptions maintains options to manage behavior of Generate.
+type CsrfOptions struct {
+	// The global secret value used to generate Tokens.
+	Secret string
+	// Cookie value used to set and get token.
+	Cookie string
+	// Cookie domain.
+	CookieDomain string
+	// Cookie path.
+	CookiePath     string
+	CookieHTTPOnly bool
+	// SameSite set the cookie SameSite type
+	SameSite http.SameSite
+	// Set the Secure flag to true on the cookie.
+	Secure bool
+	// sessionKey is the key used for getting the unique ID per user.
+	sessionKey string
+	// oldSessionKey saves old value corresponding to sessionKey.
+	oldSessionKey string
+}
+
+func newCsrfCookie(opt *CsrfOptions, value string) *http.Cookie {
+	return &http.Cookie{
+		Name:     opt.Cookie,
+		Value:    value,
+		Path:     opt.CookiePath,
+		Domain:   opt.CookieDomain,
+		MaxAge:   int(CsrfTokenTimeout.Seconds()),
+		Secure:   opt.Secure,
+		HttpOnly: opt.CookieHTTPOnly,
+		SameSite: opt.SameSite,
+	}
+}
+
+func NewCSRFProtector(opt CsrfOptions) CSRFProtector {
+	if opt.Secret == "" {
+		panic("CSRF secret is empty but it must be set") // it shouldn't happen because it is always set in code
+	}
+	opt.Cookie = util.IfZero(opt.Cookie, "_csrf")
+	opt.CookiePath = util.IfZero(opt.CookiePath, "/")
+	opt.sessionKey = "uid"
+	opt.oldSessionKey = "_old_" + opt.sessionKey
+	return &csrfProtector{opt: opt}
+}
+
+func (c *csrfProtector) PrepareForSessionUser(ctx *Context) {
+	c.id = "0"
+	if uidAny := ctx.Session.Get(c.opt.sessionKey); uidAny != nil {
+		switch uidVal := uidAny.(type) {
+		case string:
+			c.id = uidVal
+		case int64:
+			c.id = strconv.FormatInt(uidVal, 10)
+		default:
+			log.Error("invalid uid type in session: %T", uidAny)
+		}
+	}
+
+	oldUID := ctx.Session.Get(c.opt.oldSessionKey)
+	uidChanged := oldUID == nil || oldUID.(string) != c.id
+	cookieToken := ctx.GetSiteCookie(c.opt.Cookie)
+
+	needsNew := true
+	if uidChanged {
+		_ = ctx.Session.Set(c.opt.oldSessionKey, c.id)
+	} else if cookieToken != "" {
+		// If cookie token presents, reuse existing unexpired token, else generate a new one.
+		if issueTime, ok := ParseCsrfToken(cookieToken); ok {
+			dur := time.Since(issueTime) // issueTime is not a monotonic-clock, the server time may change a lot to an early time.
+			if dur >= -CsrfTokenRegenerationInterval && dur <= CsrfTokenRegenerationInterval {
+				c.token = cookieToken
+				needsNew = false
+			}
+		}
+	}
+
+	if needsNew {
+		// FIXME: actionId.
+		c.token = GenerateCsrfToken(c.opt.Secret, c.id, "POST", time.Now())
+		cookie := newCsrfCookie(&c.opt, c.token)
+		ctx.Resp.Header().Add("Set-Cookie", cookie.String())
+	}
+
+	ctx.Data["CsrfToken"] = c.token
+	ctx.Data["CsrfTokenHtml"] = template.HTML(`<input type="hidden" name="_csrf" value="` + template.HTMLEscapeString(c.token) + `">`)
+}
+
+func (c *csrfProtector) validateToken(ctx *Context, token string) {
+	if !ValidCsrfToken(token, c.opt.Secret, c.id, "POST", time.Now()) {
+		c.DeleteCookie(ctx)
+		// currently, there should be no access to the APIPath with CSRF token. because templates shouldn't use the `/api/` endpoints.
+		// FIXME: distinguish what the response is for: HTML (web page) or JSON (fetch)
+		http.Error(ctx.Resp, CsrfErrorString, http.StatusBadRequest)
+	}
+}
+
+// Validate should be used as a per route middleware. It attempts to get a token from an "X-Csrf-Token"
+// HTTP header and then a "_csrf" form value. If one of these is found, the token will be validated.
+// If this validation fails, http.StatusBadRequest is sent.
+func (c *csrfProtector) Validate(ctx *Context) {
+	if token := ctx.Req.Header.Get(CsrfHeaderName); token != "" {
+		c.validateToken(ctx, token)
+		return
+	}
+	if token := ctx.Req.FormValue(CsrfFormName); token != "" {
+		c.validateToken(ctx, token)
+		return
+	}
+	c.validateToken(ctx, "") // no csrf token, use an empty token to respond error
+}
+
+func (c *csrfProtector) DeleteCookie(ctx *Context) {
+	cookie := newCsrfCookie(&c.opt, "")
+	cookie.MaxAge = -1
+	ctx.Resp.Header().Add("Set-Cookie", cookie.String())
+}