95 lines
2.3 KiB
Go
95 lines
2.3 KiB
Go
package jwt
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import (
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"crypto"
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"crypto/hmac"
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"errors"
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)
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// Implements the HMAC-SHA family of signing methods signing methods
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type SigningMethodHMAC struct {
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Name string
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Hash crypto.Hash
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}
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// Specific instances for HS256 and company
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var (
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SigningMethodHS256 *SigningMethodHMAC
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SigningMethodHS384 *SigningMethodHMAC
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SigningMethodHS512 *SigningMethodHMAC
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ErrSignatureInvalid = errors.New("signature is invalid")
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)
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func init() {
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// HS256
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SigningMethodHS256 = &SigningMethodHMAC{"HS256", crypto.SHA256}
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RegisterSigningMethod(SigningMethodHS256.Alg(), func() SigningMethod {
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return SigningMethodHS256
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})
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// HS384
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SigningMethodHS384 = &SigningMethodHMAC{"HS384", crypto.SHA384}
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RegisterSigningMethod(SigningMethodHS384.Alg(), func() SigningMethod {
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return SigningMethodHS384
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})
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// HS512
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SigningMethodHS512 = &SigningMethodHMAC{"HS512", crypto.SHA512}
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RegisterSigningMethod(SigningMethodHS512.Alg(), func() SigningMethod {
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return SigningMethodHS512
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})
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}
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func (m *SigningMethodHMAC) Alg() string {
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return m.Name
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}
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// Verify the signature of HSXXX tokens. Returns nil if the signature is valid.
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func (m *SigningMethodHMAC) Verify(signingString, signature string, key interface{}) error {
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// Verify the key is the right type
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keyBytes, ok := key.([]byte)
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if !ok {
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return ErrInvalidKeyType
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}
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// Decode signature, for comparison
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sig, err := DecodeSegment(signature)
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if err != nil {
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return err
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}
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// Can we use the specified hashing method?
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if !m.Hash.Available() {
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return ErrHashUnavailable
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}
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// This signing method is symmetric, so we validate the signature
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// by reproducing the signature from the signing string and key, then
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// comparing that against the provided signature.
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hasher := hmac.New(m.Hash.New, keyBytes)
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hasher.Write([]byte(signingString))
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if !hmac.Equal(sig, hasher.Sum(nil)) {
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return ErrSignatureInvalid
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}
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// No validation errors. Signature is good.
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return nil
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}
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// Implements the Sign method from SigningMethod for this signing method.
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// Key must be []byte
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func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) (string, error) {
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if keyBytes, ok := key.([]byte); ok {
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if !m.Hash.Available() {
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return "", ErrHashUnavailable
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}
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hasher := hmac.New(m.Hash.New, keyBytes)
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hasher.Write([]byte(signingString))
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return EncodeSegment(hasher.Sum(nil)), nil
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}
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return "", ErrInvalidKey
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}
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