CSRF

cmd/owl/reset_password.go

@@ -3,7 +3,6 @@ package main
 import (
 	"fmt"
 	"h4kor/owl-blogs"
-	"math/rand"
 
 	"github.com/spf13/cobra"
 )
@@ -35,14 +34,7 @@ var resetPasswordCmd = &cobra.Command{
 		}
 
 		// generate a random password and print it
-		const chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
-
-		b := make([]byte, 16)
-		for i := range b {
-			b[i] = chars[rand.Intn(len(chars))]
-		}
-		password := string(b)
-
+		password := owl.GenerateRandomString(16)
 		user.ResetPassword(password)
 
 		fmt.Println("User:         ", user.Name())

cmd/owl/web/auth_test.go

@@ -16,6 +16,8 @@ func TestAuthPostWrongPassword(t *testing.T) {
 	repo, user := getSingleUserTestRepo()
 	user.ResetPassword("testpassword")
 
+	csrfToken := "test_csrf_token"
+
 	// Create Request and Response
 	form := url.Values{}
 	form.Add("password", "wrongpassword")
@@ -23,9 +25,12 @@ func TestAuthPostWrongPassword(t *testing.T) {
 	form.Add("redirect_uri", "http://example.com/response")
 	form.Add("response_type", "code")
 	form.Add("state", "test_state")
+	form.Add("csrf_token", csrfToken)
+
 	req, err := http.NewRequest("POST", user.AuthUrl()+"verify/", strings.NewReader(form.Encode()))
 	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
 	req.Header.Add("Content-Length", strconv.Itoa(len(form.Encode())))
+	req.AddCookie(&http.Cookie{Name: "csrf_token", Value: csrfToken})
 	assertions.AssertNoError(t, err, "Error creating request")
 	rr := httptest.NewRecorder()
 	router := main.SingleUserRouter(&repo)
@@ -39,6 +44,8 @@ func TestAuthPostCorrectPassword(t *testing.T) {
 	repo, user := getSingleUserTestRepo()
 	user.ResetPassword("testpassword")
 
+	csrfToken := "test_csrf_token"
+
 	// Create Request and Response
 	form := url.Values{}
 	form.Add("password", "testpassword")
@@ -46,9 +53,11 @@ func TestAuthPostCorrectPassword(t *testing.T) {
 	form.Add("redirect_uri", "http://example.com/response")
 	form.Add("response_type", "code")
 	form.Add("state", "test_state")
+	form.Add("csrf_token", csrfToken)
 	req, err := http.NewRequest("POST", user.AuthUrl()+"verify/", strings.NewReader(form.Encode()))
 	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
 	req.Header.Add("Content-Length", strconv.Itoa(len(form.Encode())))
+	req.AddCookie(&http.Cookie{Name: "csrf_token", Value: csrfToken})
 	assertions.AssertNoError(t, err, "Error creating request")
 	rr := httptest.NewRecorder()
 	router := main.SingleUserRouter(&repo)

cmd/owl/web/handler.go

@@ -100,6 +100,15 @@ func userAuthHandler(repo *owl.Repository) func(http.ResponseWriter, *http.Reque
 			return
 		}
 
+		// Double Submit Cookie Pattern
+		// https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html#double-submit-cookie
+		csrfToken := owl.GenerateRandomString(32)
+		cookie := http.Cookie{
+			Name:  "csrf_token",
+			Value: csrfToken,
+		}
+		http.SetCookie(w, &cookie)
+
 		reqData := owl.AuthRequestData{
 			Me:           me,
 			ClientId:     clientId,
@@ -107,6 +116,7 @@ func userAuthHandler(repo *owl.Repository) func(http.ResponseWriter, *http.Reque
 			State:        state,
 			ResponseType: responseType,
 			User:         user,
+			CsrfToken:    csrfToken,
 		}
 
 		html, err := owl.RenderUserAuthPage(reqData)
@@ -204,6 +214,23 @@ func userAuthVerifyHandler(repo *owl.Repository) func(http.ResponseWriter, *http
 		response_type := r.FormValue("response_type")
 		state := r.FormValue("state")
 
+		// CSRF check
+		formCsrfToken := r.FormValue("csrf_token")
+		cookieCsrfToken, err := r.Cookie("csrf_token")
+
+		if err != nil {
+			println("Error getting csrf token from cookie: ", err.Error())
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte("Error getting csrf token from cookie"))
+			return
+		}
+		if formCsrfToken != cookieCsrfToken.Value {
+			println("Invalid csrf token")
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte("Invalid csrf token"))
+			return
+		}
+
 		password_valid := user.VerifyPassword(password)
 		if !password_valid {
 			http.Redirect(w, r,

embed/auth.html

@@ -7,5 +7,6 @@
     <input type="hidden" name="redirect_uri" value="{{.RedirectUri}}">
     <input type="hidden" name="response_type" value="{{.ResponseType}}">
     <input type="hidden" name="state" value="{{.State}}">
+    <input type="hidden" name="csrf_token" value="{{.CsrfToken}}">
     <input type="submit" value="Login">
 </form>

renderer.go

@@ -27,6 +27,7 @@ type AuthRequestData struct {
 	State        string
 	ResponseType string
 	User         User
+	CsrfToken    string
 }
 
 func renderEmbedTemplate(templateFile string, data interface{}) (string, error) {

user.go

@@ -2,7 +2,6 @@ package owl
 
 import (
 	"fmt"
-	"math/rand"
 	"net/url"
 	"os"
 	"path"
@@ -287,12 +286,7 @@ func (user User) addAuthCode(code AuthCode) error {
 
 func (user User) GenerateAuthCode(client_id string, redirect_uri string) (string, error) {
 	// generate code
-	const chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
-	b := make([]byte, 32)
-	for i := range b {
-		b[i] = chars[rand.Intn(len(chars))]
-	}
-	code := string(b)
+	code := GenerateRandomString(32)
 	return code, user.addAuthCode(AuthCode{
 		Code:        code,
 		ClientId:    client_id,

utils.go

@@ -0,0 +1,16 @@
+package owl
+
+import (
+	"crypto/rand"
+	"math/big"
+)
+
+func GenerateRandomString(length int) string {
+	chars := []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
+	b := make([]rune, length)
+	for i := range b {
+		k, _ := rand.Int(rand.Reader, big.NewInt(int64(len(chars))))
+		b[i] = chars[k.Int64()]
+	}
+	return string(b)
+}