tokens_handlers.go

// 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.

package tokens

import (
	"errors"
	"strconv"
	"strings"
	"time"
)

// GetUserFromToken returns the user associated with the token
// Returns the error if something goes wrong.
// Warning: Does not validate the token. Use ValidateToken for that.
func GetUserFromToken(token string) (user string, err error) {
	mac, err := deSerializeMacaroon(token)
	if err != nil {
		return
	}

	user = string(mac.Id()[:])
	return
}

// ValidateToken validates that the token is parseable and signed by this server.
// Returns an error if the token is invalid, otherwise nil.
func ValidateToken(op TokenOptions, token string) error {
	mac, err := deSerializeMacaroon(token)
	if err != nil {
		return errors.New("Token does not represent a valid macaroon")
	}

	caveats, err := mac.VerifySignature(op.ServerPrivateKey, nil)
	if err != nil {
		return errors.New("Provided token was not issued by this server")
	}

	err = verifyCaveats(caveats, op.UserID)
	if err != nil {
		return errors.New("Provided token not authorized")
	}
	return nil
}

// verifyCaveats verifies caveats associated with a login token macaroon.
// which are "gen = 1", "user_id = ...", "time < ..."
// Returns nil on successful verification, else returns an error.
func verifyCaveats(caveats []string, userID string) error {
	// variable verified represents a bitmap
	// last 4 bits are Uvvv where,
	// U: unknownCaveat
	// v: caveat to be verified
	var verified uint8
	now := time.Now().Second()

LoopCaveat:
	for _, caveat := range caveats {
		switch {
		case caveat == Gen:
			verified |= 1
		case strings.HasPrefix(caveat, UserPrefix):
			if caveat[len(UserPrefix):] == userID {
				verified |= 2
			}
		case strings.HasPrefix(caveat, TimePrefix):
			if verifyExpiry(caveat[len(TimePrefix):], now) {
				verified |= 4
			}
		default:
			verified |= 8
			break LoopCaveat
		}
	}
	// Check that all three caveats are verified and no extra caveats
	// i.e. Uvvv == 0111
	if verified == 7 {
		return nil
	} else if verified >= 8 {
		return errors.New("Unknown caveat present")
	}

	return errors.New("Required caveats not present")
}

func verifyExpiry(t string, now int) bool {
	expiry, err := strconv.Atoi(t)

	if err != nil {
		return false
	}
	return now < expiry
}