feat: add caldav tokens (#1065)

# Description

This PR adds API routes to create and manage caldav tokens. These tokens can be used instead of a user password - required for users who are using external auth providers and don't have a password.

Fixes #842

Frontend: https://kolaente.dev/vikunja/frontend/pulls/1186

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/1065

pkg/routes/caldav/auth.go

@@ -0,0 +1,70 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package caldav
+
+import (
+	"errors"
+
+	"code.vikunja.io/api/pkg/db"
+	"code.vikunja.io/api/pkg/log"
+	"code.vikunja.io/api/pkg/user"
+
+	"github.com/labstack/echo/v4"
+	"golang.org/x/crypto/bcrypt"
+)
+
+func BasicAuth(username, password string, c echo.Context) (bool, error) {
+	creds := &user.Login{
+		Username: username,
+		Password: password,
+	}
+	s := db.NewSession()
+	defer s.Close()
+	u, err := user.CheckUserCredentials(s, creds)
+	if err != nil && !user.IsErrWrongUsernameOrPassword(err) {
+		log.Errorf("Error during basic auth for caldav: %v", err)
+		return false, nil
+	}
+
+	if err == nil {
+		c.Set("userBasicAuth", u)
+		return true, nil
+	}
+
+	tokens, err := user.GetCaldavTokens(u)
+	if err != nil {
+		log.Errorf("Error while getting tokens for caldav auth: %v", err)
+		return false, nil
+	}
+
+	// Looping over all tokens until we find one that matches
+	for _, token := range tokens {
+		err = bcrypt.CompareHashAndPassword([]byte(token.Token), []byte(password))
+		if err != nil {
+			if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
+				continue
+			}
+			log.Errorf("Error while verifying tokens for caldav auth: %v", err)
+			return false, nil
+		}
+
+		c.Set("userBasicAuth", u)
+		return true, nil
+	}
+
+	return false, nil
+}