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// Copyright 2022 Google LLC
//
// 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 jwt
import (
"fmt"
"time"
)
const (
jwtMaxClockSkewMinutes = 10
)
// ValidatorOpts define validation options for JWT validators.
type ValidatorOpts struct {
ExpectedTypeHeader *string
ExpectedIssuer *string
ExpectedAudience *string
IgnoreTypeHeader bool
IgnoreAudiences bool
IgnoreIssuer bool
AllowMissingExpiration bool
ExpectIssuedInThePast bool
ClockSkew time.Duration
FixedNow time.Time
// Deprecated: Use ExpectedAudience instead.
ExpectedAudiences *string
}
// Validator defines how JSON Web Tokens (JWT) should be validated.
type Validator struct {
opts ValidatorOpts
}
// NewValidator creates a new Validator.
func NewValidator(opts *ValidatorOpts) (*Validator, error) {
if opts == nil {
return nil, fmt.Errorf("ValidatorOpts can't be nil")
}
if opts.ExpectedAudiences != nil {
if opts.ExpectedAudience != nil {
return nil, fmt.Errorf("ExpectedAudiences and ExpectedAudience can't be set at the same time")
}
opts.ExpectedAudience = opts.ExpectedAudiences
opts.ExpectedAudiences = nil
}
if opts.ExpectedTypeHeader != nil && opts.IgnoreTypeHeader {
return nil, fmt.Errorf("ExpectedTypeHeader and IgnoreTypeHeader cannot be used together")
}
if opts.ExpectedIssuer != nil && opts.IgnoreIssuer {
return nil, fmt.Errorf("ExpectedIssuer and IgnoreIssuer cannot be used together")
}
if opts.ExpectedAudience != nil && opts.IgnoreAudiences {
return nil, fmt.Errorf("ExpectedAudience and IgnoreAudience cannot be used together")
}
if opts.ClockSkew.Minutes() > jwtMaxClockSkewMinutes {
return nil, fmt.Errorf("clock skew too large, max is %d minutes", jwtMaxClockSkewMinutes)
}
return &Validator{
opts: *opts,
}, nil
}
// Validate validates a rawJWT according to the options provided.
func (v *Validator) Validate(rawJWT *RawJWT) error {
if rawJWT == nil {
return fmt.Errorf("rawJWT can't be nil")
}
if err := v.validateTimestamps(rawJWT); err != nil {
return err
}
if err := v.validateTypeHeader(rawJWT); err != nil {
return fmt.Errorf("validating type header: %v", err)
}
if err := v.validateAudiences(rawJWT); err != nil {
return fmt.Errorf("validating audience claim: %v", err)
}
if err := v.validateIssuer(rawJWT); err != nil {
return fmt.Errorf("validating issuer claim: %v", err)
}
return nil
}
func (v *Validator) validateTimestamps(rawJWT *RawJWT) error {
now := time.Now()
if !v.opts.FixedNow.IsZero() {
now = v.opts.FixedNow
}
if !rawJWT.HasExpiration() && !v.opts.AllowMissingExpiration {
return fmt.Errorf("token doesn't have an expiration set")
}
if rawJWT.HasExpiration() {
exp, err := rawJWT.ExpiresAt()
if err != nil {
return err
}
if !exp.After(now.Add(-v.opts.ClockSkew)) {
return errJwtExpired
}
}
if rawJWT.HasNotBefore() {
nbf, err := rawJWT.NotBefore()
if err != nil {
return err
}
if nbf.After(now.Add(v.opts.ClockSkew)) {
return fmt.Errorf("token cannot be used yet")
}
}
if v.opts.ExpectIssuedInThePast {
iat, err := rawJWT.IssuedAt()
if err != nil {
return err
}
if iat.After(now.Add(v.opts.ClockSkew)) {
return fmt.Errorf("token has an invalid iat claim in the future")
}
}
return nil
}
func (v *Validator) validateTypeHeader(rawJWT *RawJWT) error {
skip, err := validateFieldPresence(v.opts.IgnoreTypeHeader, rawJWT.HasTypeHeader(), v.opts.ExpectedTypeHeader != nil)
if err != nil {
return err
}
if skip {
return nil
}
typeHeader, err := rawJWT.TypeHeader()
if err != nil {
return err
}
if typeHeader != *v.opts.ExpectedTypeHeader {
return fmt.Errorf("wrong 'type header' type")
}
return nil
}
func (v *Validator) validateIssuer(rawJWT *RawJWT) error {
skip, err := validateFieldPresence(v.opts.IgnoreIssuer, rawJWT.HasIssuer(), v.opts.ExpectedIssuer != nil)
if err != nil {
return err
}
if skip {
return nil
}
issuer, err := rawJWT.Issuer()
if err != nil {
return err
}
if issuer != *v.opts.ExpectedIssuer {
return fmt.Errorf("got %s, want %s", issuer, *v.opts.ExpectedIssuer)
}
return nil
}
func (v *Validator) validateAudiences(rawJWT *RawJWT) error {
skip, err := validateFieldPresence(v.opts.IgnoreAudiences, rawJWT.HasAudiences(), v.opts.ExpectedAudience != nil)
if err != nil {
return err
}
if skip {
return nil
}
audiences, err := rawJWT.Audiences()
if err != nil {
return err
}
for i, aud := range audiences {
if aud == *v.opts.ExpectedAudience {
break
}
if i == len(audiences)-1 {
return fmt.Errorf("%s not found", *v.opts.ExpectedAudience)
}
}
return nil
}
func validateFieldPresence(ignore bool, isPresent bool, isExpected bool) (bool, error) {
if ignore {
return true, nil
}
if !isExpected && !isPresent {
return true, nil
}
if !isExpected && isPresent {
return false, fmt.Errorf("token has claim but validator doesn't expect it")
}
if isExpected && !isPresent {
return false, fmt.Errorf("claim was expected but isn't present")
}
return false, nil
}
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