72 lines
1.7 KiB
Go
72 lines
1.7 KiB
Go
package authproxy
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"crypto/sha256"
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"encoding/base64"
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"encoding/hex"
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"encoding/json"
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"fmt"
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"io"
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)
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// box seals and opens small JSON payloads with AES-256-GCM. The purpose
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// string is bound in as additional authenticated data so a token minted for
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// one use (e.g. OAuth state) can never be replayed as another (e.g. a
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// session cookie).
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type box struct {
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aead cipher.AEAD
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}
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func newBox(secret string) (*box, error) {
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key := sha256.Sum256([]byte(secret))
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block, err := aes.NewCipher(key[:])
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if err != nil {
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return nil, err
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}
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aead, err := cipher.NewGCM(block)
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if err != nil {
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return nil, err
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}
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return &box{aead: aead}, nil
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}
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func (b *box) seal(purpose string, v any) (string, error) {
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plain, err := json.Marshal(v)
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if err != nil {
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return "", err
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}
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nonce := make([]byte, b.aead.NonceSize())
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if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
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return "", err
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}
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out := b.aead.Seal(nonce, nonce, plain, []byte(purpose))
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return base64.RawURLEncoding.EncodeToString(out), nil
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}
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func (b *box) open(purpose, token string, v any) error {
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raw, err := base64.RawURLEncoding.DecodeString(token)
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if err != nil {
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return fmt.Errorf("malformed token: %w", err)
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}
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ns := b.aead.NonceSize()
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if len(raw) <= ns {
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return fmt.Errorf("malformed token: too short")
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}
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plain, err := b.aead.Open(nil, raw[:ns], raw[ns:], []byte(purpose))
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if err != nil {
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return fmt.Errorf("token failed authentication: %w", err)
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}
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return json.Unmarshal(plain, v)
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}
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func randToken() string {
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buf := make([]byte, 16)
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if _, err := io.ReadFull(rand.Reader, buf); err != nil {
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panic(err) // crypto/rand failure is unrecoverable
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}
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return hex.EncodeToString(buf)
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}
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