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jwt.go
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jwt.go
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package token
import (
"crypto/ecdsa"
"crypto/elliptic"
"encoding/base64"
"errors"
"math/big"
"net/url"
"path"
"strings"
"time"
"github.com/golang-jwt/jwt/v5"
)
type JWT jwt.Token
func parseBase64(k string, d map[string]interface{}) ([]byte, error) {
v, ok := d[k].(string)
if !ok {
return nil, errors.New("key " + k + " not found")
}
vv, err := base64.RawURLEncoding.DecodeString(v)
if err != nil {
return nil, err
}
return vv, nil
}
func ParseKey(key map[string]interface{}) (interface{}, error) {
kty, ok := key["kty"].(string)
if !ok {
return nil, errors.New("kty not found")
}
alg, ok := key["alg"].(string)
if !ok {
return nil, errors.New("alg not found")
}
switch kty {
case "oct":
var length int
switch alg {
case "HS256":
length = 32
case "HS384":
length = 48
case "HS512":
length = 64
default:
return nil, errors.New("unknown alg")
}
k, err := parseBase64("k", key)
if err != nil {
return nil, err
}
if len(k) != length {
return nil, errors.New("bad length for key")
}
return k, nil
case "EC":
if alg != "ES256" {
return nil, errors.New("uknown alg")
}
crv, ok := key["crv"].(string)
if !ok {
return nil, errors.New("crv not found")
}
if crv != "P-256" {
return nil, errors.New("unknown crv")
}
curve := elliptic.P256()
xbytes, err := parseBase64("x", key)
if err != nil {
return nil, err
}
var x big.Int
x.SetBytes(xbytes)
ybytes, err := parseBase64("y", key)
if err != nil {
return nil, err
}
var y big.Int
y.SetBytes(ybytes)
if !curve.IsOnCurve(&x, &y) {
return nil, errors.New("key is not on curve")
}
return &ecdsa.PublicKey{
Curve: curve,
X: &x,
Y: &y,
}, nil
default:
return nil, errors.New("unknown key type")
}
}
func getKey(header map[string]interface{}, keys []map[string]interface{}) (interface{}, error) {
alg, _ := header["alg"].(string)
kid, _ := header["kid"].(string)
for _, k := range keys {
kid2, _ := k["kid"].(string)
alg2, _ := k["alg"].(string)
if (kid == "" || kid == kid2) && alg == alg2 {
return ParseKey(k)
}
}
return nil, errors.New("key not found")
}
func toStringArray(a interface{}) ([]string, bool) {
aa, ok := a.([]interface{})
if !ok {
return nil, false
}
b := make([]string, len(aa))
for i, v := range aa {
w, ok := v.(string)
if !ok {
return nil, false
}
b[i] = w
}
return b, true
}
func parseJWT(token string, keys []map[string]interface{}) (*JWT, error) {
t, err := jwt.Parse(
token,
func(t *jwt.Token) (interface{}, error) {
return getKey(t.Header, keys)
},
jwt.WithExpirationRequired(),
jwt.WithIssuedAt(),
jwt.WithLeeway(5*time.Second),
)
if err != nil {
if errors.Is(err, jwt.ErrTokenMalformed) {
// assume this is not a JWT
return nil, nil
}
return nil, err
}
return (*JWT)(t), nil
}
func (token *JWT) Check(host, group string, username *string) (string, []string, error) {
sub, err := token.Claims.GetSubject()
if err != nil {
return "", nil, err
}
// we accept tokens with a different username from the one provided,
// and use the token's 'sub' field to override the username
aud, err := token.Claims.GetAudience()
if err != nil {
return "", nil, err
}
ok := false
for _, u := range aud {
url, err := url.Parse(u)
if err != nil {
continue
}
// if canonicalHost is not set, we allow tokens
// for any domain name. Hopefully different
// servers use distinct keys.
if host != "" {
if !strings.EqualFold(url.Host, host) {
continue
}
}
if url.Path == path.Join("/group", group)+"/" {
ok = true
break
}
}
if !ok {
return "", nil, errors.New("token for wrong group")
}
claims, ok := token.Claims.(jwt.MapClaims)
if !ok {
return "", nil, errors.New("unexpected type for token")
}
var perms []string
if p, ok := claims["permissions"]; ok && p != nil {
perms, ok = toStringArray(p)
if !ok {
return "", nil, errors.New("invalid 'permissions' field")
}
}
return sub, perms, nil
}