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// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package oidc implements support for fetching OIDC tokens
package oidc
import (
"context"
"errors"
"fmt"
"net"
"net/http"
"net/url"
"os"
"time"
coreoidc "github.com/coreos/go-oidc/v3/oidc"
"github.com/pkg/browser"
"github.com/segmentio/ksuid"
"github.com/sigstore/sigstore/pkg/oauth"
"golang.org/x/oauth2"
)
const oobRedirectURI = "urn:ietf:wg:oauth:2.0:oob"
type browserOpener func(url string) error
func doOobFlow(cfg *oauth2.Config, stateToken string, opts []oauth2.AuthCodeOption) string {
cfg.RedirectURL = oobRedirectURI
authURL := cfg.AuthCodeURL(stateToken, opts...)
fmt.Fprintln(os.Stderr, "Go to the following link in a browser:\n\n\t", authURL)
fmt.Fprintf(os.Stderr, "Enter verification code: ")
var code string
fmt.Scanln(&code)
return code
}
func startRedirectListener(state, htmlPage, redirectURL string, codeCh chan string, errCh chan error) (*http.Server, *url.URL, error) {
var listener net.Listener
var urlListener *url.URL
var err error
if redirectURL == "" {
listener, err = net.Listen("tcp", "localhost:0") // ":0" == OS picks
if err != nil {
return nil, nil, err
}
addr, ok := listener.Addr().(*net.TCPAddr)
if !ok {
return nil, nil, fmt.Errorf("listener addr is not TCPAddr")
}
urlListener = &url.URL{
Scheme: "http",
Host: fmt.Sprintf("localhost:%d", addr.Port),
Path: "/auth/callback",
}
} else {
urlListener, err = url.Parse(redirectURL)
if err != nil {
return nil, nil, err
}
listener, err = net.Listen("tcp", urlListener.Host)
if err != nil {
return nil, nil, err
}
}
m := http.NewServeMux()
s := &http.Server{
Addr: urlListener.Host,
Handler: m,
// an arbitrary reasonable value to fix gosec lint error
ReadHeaderTimeout: 2 * time.Second,
}
m.HandleFunc(urlListener.Path, func(w http.ResponseWriter, r *http.Request) {
// even though these are fetched from the FormValue method,
// these are supplied as query parameters
if r.FormValue("state") != state {
errCh <- errors.New("invalid state token")
return
}
codeCh <- r.FormValue("code")
fmt.Fprint(w, htmlPage)
})
go func() {
if err := s.Serve(listener); err != nil && !errors.Is(err, http.ErrServerClosed) {
errCh <- err
}
}()
return s, urlListener, nil
}
func getCode(codeCh chan string, errCh chan error) (string, error) {
select {
case code := <-codeCh:
return code, nil
case err := <-errCh:
return "", err
case <-time.After(120 * time.Second):
return "", errors.New("timeout")
}
}
// newKSUID returns a globally unique, base62 (URL-safe) encoded, 27 character string.
func newKSUID() string {
return ksuid.New().String()
}
type interactiveIDTokenSource struct {
cfg oauth2.Config
oidp *coreoidc.Provider
extraAuthCodeOpts []oauth2.AuthCodeOption
browser browserOpener
}
var errWontOpenBrowser = errors.New("not opening that browser")
func failBrowser(string) error {
return errWontOpenBrowser
}
func (idts *interactiveIDTokenSource) IDToken(ctx context.Context) (*IDToken, error) {
cfg := idts.cfg
p := idts.oidp
// generate random fields and save them for comparison after OAuth2 dance
stateToken := newKSUID()
nonce := newKSUID()
codeCh := make(chan string)
errCh := make(chan error)
// starts listener using the redirect_uri, otherwise starts on ephemeral port
redirectServer, redirectURL, err := startRedirectListener(stateToken, oauth.InteractiveSuccessHTML, cfg.RedirectURL, codeCh, errCh)
if err != nil {
close(codeCh)
close(errCh)
return nil, fmt.Errorf("starting redirect listener: %w", err)
}
defer func() {
go func() {
_ = redirectServer.Shutdown(context.Background())
close(codeCh)
close(errCh)
}()
}()
cfg.RedirectURL = redirectURL.String()
// require that OIDC provider support PKCE to provide sufficient security for the CLI
pkce, err := NewPKCE(p)
if err != nil {
return nil, err
}
opts := append(pkce.AuthURLOpts(), oauth2.AccessTypeOnline, coreoidc.Nonce(nonce))
if len(idts.extraAuthCodeOpts) > 0 {
opts = append(opts, idts.extraAuthCodeOpts...)
}
authCodeURL := cfg.AuthCodeURL(stateToken, opts...)
var code string
if err := idts.browser(authCodeURL); err != nil {
// Swap to the out of band flow if we can't open the browser
if !errors.Is(err, errWontOpenBrowser) {
fmt.Fprintf(os.Stderr, "error opening browser: %v\n", err)
}
code = doOobFlow(&cfg, stateToken, opts)
} else {
fmt.Fprintf(os.Stderr, "Your browser will now be opened to:\n%s\n", authCodeURL)
code, err = getCode(codeCh, errCh)
if err != nil {
fmt.Fprintf(os.Stderr, "error getting code from local server: %v\n", err)
code = doOobFlow(&cfg, stateToken, opts)
}
}
token, err := cfg.Exchange(ctx, code, append(pkce.TokenURLOpts(), coreoidc.Nonce(nonce))...)
if err != nil {
return nil, err
}
verifier := p.Verifier(&coreoidc.Config{ClientID: cfg.ClientID})
return extractAndVerifyIDToken(ctx, token, verifier, nonce)
}
// InteractiveIDTokenSource returns an `IDTokenSource` which performs an interactive Oauth token flow in order to retrieve an `IDToken`.
func InteractiveIDTokenSource(cfg oauth2.Config, oidp *coreoidc.Provider, extraAuthCodeOpts []oauth2.AuthCodeOption, allowBrowser bool) IDTokenSource {
ts := &interactiveIDTokenSource{cfg: cfg, oidp: oidp, extraAuthCodeOpts: extraAuthCodeOpts, browser: failBrowser}
if allowBrowser {
ts.browser = browser.OpenURL
}
return ts
}
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