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verifier.go
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verifier.go
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package googleIDVerifier
import (
"fmt"
"time"
"golang.org/x/oauth2/jws"
)
var (
// MaxTokenLifetime is one day
MaxTokenLifetime = time.Second * 86400
// ClockSkew - five minutes
ClockSkew = time.Minute * 5
// Issuers is the allowed oauth token issuers
Issuers = []string{
"accounts.google.com",
"https://accounts.google.com",
}
)
// TokenVerifier has a method to verify a Google-issued OAuth2 token ID
type TokenVerifier interface {
// VerifyIDToken checks the validity of a given Google-issued OAuth2 token ID
VerifyIDToken(idToken string, audience ...string) error
}
// CertsVerifier implements Verifier by fetching once in a while the Google certs and validating the ID tokens locally
type CertsVerifier struct {
DefaultAudience []string
}
// VerifyIDToken checks the validity of a given Google-issued OAuth2 token ID
func (v *CertsVerifier) VerifyIDToken(idToken string, audience ...string) error {
certs, err := getFederatedSignonCerts()
if err != nil {
return err
}
if len(audience) == 0 {
audience = v.DefaultAudience
}
return VerifySignedJWTWithCerts(idToken, certs, audience, Issuers, MaxTokenLifetime)
}
// VerifySignedJWTWithCerts is golang port of OAuth2Client.prototype.verifySignedJwtWithCerts
func VerifySignedJWTWithCerts(token string, certs *Certs, allowedAuds []string, issuers []string, maxExpiry time.Duration) error {
header, claimSet, err := parseJWT(token)
if err != nil {
return err
}
key := certs.Keys[header.KeyID]
if key == nil {
return ErrPublicKeyNotFound
}
err = jws.Verify(token, key)
if err != nil {
return ErrWrongSignature
}
if claimSet.Iat < 1 {
return ErrNoIssueTimeInToken
}
if claimSet.Exp < 1 {
return ErrNoExpirationTimeInToken
}
now := nowFn()
if claimSet.Exp > now.Unix()+int64(maxExpiry.Seconds()) {
return ErrExpirationTimeTooFarInFuture
}
earliest := claimSet.Iat - int64(ClockSkew.Seconds())
latest := claimSet.Exp + int64(ClockSkew.Seconds())
if now.Unix() < earliest {
return ErrTokenUsedTooEarly
}
if now.Unix() > latest {
return ErrTokenUsedTooLate
}
found := false
for _, issuer := range issuers {
if issuer == claimSet.Iss {
found = true
break
}
}
if !found {
return fmt.Errorf("Wrong issuer: %s", claimSet.Iss)
}
audFound := false
for _, aud := range allowedAuds {
if aud == claimSet.Aud {
audFound = true
break
}
}
if !audFound {
return fmt.Errorf("Wrong aud: %s", claimSet.Aud)
}
return nil
}