chore: migrate to gitea

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

@@ -0,0 +1,94 @@
+// Copyright 2021 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 authhandler implements a TokenSource to support
+// "three-legged OAuth 2.0" via a custom AuthorizationHandler.
+package authhandler
+
+import (
+	"context"
+	"errors"
+
+	"golang.org/x/oauth2"
+)
+
+const (
+	// Parameter keys for AuthCodeURL method to support PKCE.
+	codeChallengeKey       = "code_challenge"
+	codeChallengeMethodKey = "code_challenge_method"
+
+	// Parameter key for Exchange method to support PKCE.
+	codeVerifierKey = "code_verifier"
+)
+
+// PKCEParams holds parameters to support PKCE.
+type PKCEParams struct {
+	Challenge       string // The unpadded, base64-url-encoded string of the encrypted code verifier.
+	ChallengeMethod string // The encryption method (ex. S256).
+	Verifier        string // The original, non-encrypted secret.
+}
+
+// AuthorizationHandler is a 3-legged-OAuth helper that prompts
+// the user for OAuth consent at the specified auth code URL
+// and returns an auth code and state upon approval.
+type AuthorizationHandler func(authCodeURL string) (code string, state string, err error)
+
+// TokenSourceWithPKCE is an enhanced version of [oauth2.TokenSource] with PKCE support.
+//
+// The pkce parameter supports PKCE flow, which uses code challenge and code verifier
+// to prevent CSRF attacks. A unique code challenge and code verifier should be generated
+// by the caller at runtime. See https://www.oauth.com/oauth2-servers/pkce/ for more info.
+func TokenSourceWithPKCE(ctx context.Context, config *oauth2.Config, state string, authHandler AuthorizationHandler, pkce *PKCEParams) oauth2.TokenSource {
+	return oauth2.ReuseTokenSource(nil, authHandlerSource{config: config, ctx: ctx, authHandler: authHandler, state: state, pkce: pkce})
+}
+
+// TokenSource returns an [oauth2.TokenSource] that fetches access tokens
+// using 3-legged-OAuth flow.
+//
+// The provided [context.Context] is used for oauth2 Exchange operation.
+//
+// The provided [oauth2.Config] should be a full configuration containing AuthURL,
+// TokenURL, and Scope.
+//
+// An environment-specific AuthorizationHandler is used to obtain user consent.
+//
+// Per the OAuth protocol, a unique "state" string should be specified here.
+// This token source will verify that the "state" is identical in the request
+// and response before exchanging the auth code for OAuth token to prevent CSRF
+// attacks.
+func TokenSource(ctx context.Context, config *oauth2.Config, state string, authHandler AuthorizationHandler) oauth2.TokenSource {
+	return TokenSourceWithPKCE(ctx, config, state, authHandler, nil)
+}
+
+type authHandlerSource struct {
+	ctx         context.Context
+	config      *oauth2.Config
+	authHandler AuthorizationHandler
+	state       string
+	pkce        *PKCEParams
+}
+
+func (source authHandlerSource) Token() (*oauth2.Token, error) {
+	// Step 1: Obtain auth code.
+	var authCodeUrlOptions []oauth2.AuthCodeOption
+	if source.pkce != nil && source.pkce.Challenge != "" && source.pkce.ChallengeMethod != "" {
+		authCodeUrlOptions = []oauth2.AuthCodeOption{oauth2.SetAuthURLParam(codeChallengeKey, source.pkce.Challenge),
+			oauth2.SetAuthURLParam(codeChallengeMethodKey, source.pkce.ChallengeMethod)}
+	}
+	url := source.config.AuthCodeURL(source.state, authCodeUrlOptions...)
+	code, state, err := source.authHandler(url)
+	if err != nil {
+		return nil, err
+	}
+	if state != source.state {
+		return nil, errors.New("state mismatch in 3-legged-OAuth flow")
+	}
+
+	// Step 2: Exchange auth code for access token.
+	var exchangeOptions []oauth2.AuthCodeOption
+	if source.pkce != nil && source.pkce.Verifier != "" {
+		exchangeOptions = []oauth2.AuthCodeOption{oauth2.SetAuthURLParam(codeVerifierKey, source.pkce.Verifier)}
+	}
+	return source.config.Exchange(source.ctx, code, exchangeOptions...)
+}