chore: migrate to gitea

vendor/golang.org/x/oauth2/pkce.go

@@ -0,0 +1,69 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package oauth2
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"net/url"
+)
+
+const (
+	codeChallengeKey       = "code_challenge"
+	codeChallengeMethodKey = "code_challenge_method"
+	codeVerifierKey        = "code_verifier"
+)
+
+// GenerateVerifier generates a PKCE code verifier with 32 octets of randomness.
+// This follows recommendations in RFC 7636.
+//
+// A fresh verifier should be generated for each authorization.
+// The resulting verifier should be passed to [Config.AuthCodeURL] or [Config.DeviceAuth]
+// with [S256ChallengeOption], and to [Config.Exchange] or [Config.DeviceAccessToken]
+// with [VerifierOption].
+func GenerateVerifier() string {
+	// "RECOMMENDED that the output of a suitable random number generator be
+	// used to create a 32-octet sequence.  The octet sequence is then
+	// base64url-encoded to produce a 43-octet URL-safe string to use as the
+	// code verifier."
+	// https://datatracker.ietf.org/doc/html/rfc7636#section-4.1
+	data := make([]byte, 32)
+	if _, err := rand.Read(data); err != nil {
+		panic(err)
+	}
+	return base64.RawURLEncoding.EncodeToString(data)
+}
+
+// VerifierOption returns a PKCE code verifier [AuthCodeOption]. It should only be
+// passed to [Config.Exchange] or [Config.DeviceAccessToken].
+func VerifierOption(verifier string) AuthCodeOption {
+	return setParam{k: codeVerifierKey, v: verifier}
+}
+
+// S256ChallengeFromVerifier returns a PKCE code challenge derived from verifier with method S256.
+//
+// Prefer to use [S256ChallengeOption] where possible.
+func S256ChallengeFromVerifier(verifier string) string {
+	sha := sha256.Sum256([]byte(verifier))
+	return base64.RawURLEncoding.EncodeToString(sha[:])
+}
+
+// S256ChallengeOption derives a PKCE code challenge from the verifier with
+// method S256. It should be passed to [Config.AuthCodeURL] or [Config.DeviceAuth]
+// only.
+func S256ChallengeOption(verifier string) AuthCodeOption {
+	return challengeOption{
+		challenge_method: "S256",
+		challenge:        S256ChallengeFromVerifier(verifier),
+	}
+}
+
+type challengeOption struct{ challenge_method, challenge string }
+
+func (p challengeOption) setValue(m url.Values) {
+	m.Set(codeChallengeMethodKey, p.challenge_method)
+	m.Set(codeChallengeKey, p.challenge)
+}