Merge pull request 'feat: implement PKCE when acting as oauth2 client (for user login)' (#3307) from oliverpool/forgejo:pkce into forgejo

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/3307
Reviewed-by: twenty-panda <twenty-panda@noreply.codeberg.org>
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
This commit is contained in:
Earl Warren 2024-04-29 10:58:17 +00:00
commit ce2becb55e
5 changed files with 119 additions and 6 deletions

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@ -0,0 +1 @@
Support [Proof Key for Code Exchange (PKCE - RFC7636)](https://www.rfc-editor.org/rfc/rfc7636) for external login sources using the OAuth2 flow.

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@ -5,6 +5,7 @@ package auth
import (
go_context "context"
"crypto/sha256"
"encoding/base64"
"errors"
"fmt"
@ -860,13 +861,19 @@ func SignInOAuth(ctx *context.Context) {
return
}
if err = authSource.Cfg.(*oauth2.Source).Callout(ctx.Req, ctx.Resp); err != nil {
codeChallenge, err := generateCodeChallenge(ctx)
if err != nil {
ctx.ServerError("SignIn", fmt.Errorf("could not generate code_challenge: %w", err))
return
}
if err = authSource.Cfg.(*oauth2.Source).Callout(ctx.Req, ctx.Resp, codeChallenge); err != nil {
if strings.Contains(err.Error(), "no provider for ") {
if err = oauth2.ResetOAuth2(ctx); err != nil {
ctx.ServerError("SignIn", err)
return
}
if err = authSource.Cfg.(*oauth2.Source).Callout(ctx.Req, ctx.Resp); err != nil {
if err = authSource.Cfg.(*oauth2.Source).Callout(ctx.Req, ctx.Resp, codeChallenge); err != nil {
ctx.ServerError("SignIn", err)
}
return
@ -1203,6 +1210,27 @@ func handleOAuth2SignIn(ctx *context.Context, source *auth.Source, u *user_model
ctx.Redirect(setting.AppSubURL + "/user/two_factor")
}
// generateCodeChallenge stores a code verifier in the session and returns a S256 code challenge for PKCE
func generateCodeChallenge(ctx *context.Context) (codeChallenge string, err error) {
codeVerifier, err := util.CryptoRandomString(43) // 256/log2(62) = 256 bits of entropy (each char having log2(62) of randomness)
if err != nil {
return "", err
}
if err = ctx.Session.Set("CodeVerifier", codeVerifier); err != nil {
return "", err
}
return encodeCodeChallenge(codeVerifier)
}
func encodeCodeChallenge(codeVerifier string) (string, error) {
hasher := sha256.New()
_, err := io.WriteString(hasher, codeVerifier)
codeChallenge := base64.RawURLEncoding.EncodeToString(hasher.Sum(nil))
return codeChallenge, err
}
// OAuth2UserLoginCallback attempts to handle the callback from the OAuth2 provider and if successful
// login the user
func oAuth2UserLoginCallback(ctx *context.Context, authSource *auth.Source, request *http.Request, response http.ResponseWriter) (*user_model.User, goth.User, error) {
gothUser, err := oAuth2FetchUser(ctx, authSource, request, response)
if err != nil {
@ -1239,7 +1267,9 @@ func oAuth2FetchUser(ctx *context.Context, authSource *auth.Source, request *htt
}
// Proceed to authenticate through goth.
gothUser, err := oauth2Source.Callback(request, response)
codeVerifier, _ := ctx.Session.Get("CodeVerifier").(string)
_ = ctx.Session.Delete("CodeVerifier")
gothUser, err := oauth2Source.Callback(request, response, codeVerifier)
if err != nil {
if err.Error() == "securecookie: the value is too long" || strings.Contains(err.Error(), "Data too long") {
log.Error("OAuth2 Provider %s returned too long a token. Current max: %d. Either increase the [OAuth2] MAX_TOKEN_LENGTH or reduce the information returned from the OAuth2 provider", authSource.Name, setting.OAuth2.MaxTokenLength)

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@ -93,3 +93,10 @@ func TestNewAccessTokenResponse_OIDCToken(t *testing.T) {
assert.Equal(t, user.Email, oidcToken.Email)
assert.Equal(t, user.IsActive, oidcToken.EmailVerified)
}
func TestEncodeCodeChallenge(t *testing.T) {
// test vector from https://datatracker.ietf.org/doc/html/rfc7636#page-18
codeChallenge, err := encodeCodeChallenge("dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk")
assert.NoError(t, err)
assert.Equal(t, "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM", codeChallenge)
}

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@ -5,16 +5,25 @@ package oauth2
import (
"net/http"
"net/url"
"github.com/markbates/goth"
"github.com/markbates/goth/gothic"
)
// Callout redirects request/response pair to authenticate against the provider
func (source *Source) Callout(request *http.Request, response http.ResponseWriter) error {
func (source *Source) Callout(request *http.Request, response http.ResponseWriter, codeChallengeS256 string) error {
// not sure if goth is thread safe (?) when using multiple providers
request.Header.Set(ProviderHeaderKey, source.authSource.Name)
var querySuffix string
if codeChallengeS256 != "" {
querySuffix = "&" + url.Values{
"code_challenge_method": []string{"S256"},
"code_challenge": []string{codeChallengeS256},
}.Encode()
}
// don't use the default gothic begin handler to prevent issues when some error occurs
// normally the gothic library will write some custom stuff to the response instead of our own nice error page
// gothic.BeginAuthHandler(response, request)
@ -24,17 +33,29 @@ func (source *Source) Callout(request *http.Request, response http.ResponseWrite
url, err := gothic.GetAuthURL(response, request)
if err == nil {
http.Redirect(response, request, url, http.StatusTemporaryRedirect)
// hacky way to set the code_challenge, but no better way until
// https://github.com/markbates/goth/issues/516 is resolved
http.Redirect(response, request, url+querySuffix, http.StatusTemporaryRedirect)
}
return err
}
// Callback handles OAuth callback, resolve to a goth user and send back to original url
// this will trigger a new authentication request, but because we save it in the session we can use that
func (source *Source) Callback(request *http.Request, response http.ResponseWriter) (goth.User, error) {
func (source *Source) Callback(request *http.Request, response http.ResponseWriter, codeVerifier string) (goth.User, error) {
// not sure if goth is thread safe (?) when using multiple providers
request.Header.Set(ProviderHeaderKey, source.authSource.Name)
if codeVerifier != "" {
// hacky way to set the code_verifier...
// Will be picked up inside CompleteUserAuth: params := req.URL.Query()
// https://github.com/markbates/goth/pull/474/files
request = request.Clone(request.Context())
q := request.URL.Query()
q.Add("code_verifier", codeVerifier)
request.URL.RawQuery = q.Encode()
}
gothRWMutex.RLock()
defer gothRWMutex.RUnlock()

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@ -6,9 +6,12 @@ package integration
import (
"bytes"
"context"
"crypto/sha256"
"encoding/base64"
"fmt"
"io"
"net/http"
"net/url"
"testing"
auth_model "code.gitea.io/gitea/models/auth"
@ -470,6 +473,57 @@ func TestSignInOAuthCallbackSignIn(t *testing.T) {
assert.Greater(t, userAfterLogin.LastLoginUnix, userGitLab.LastLoginUnix)
}
func TestSignInOAuthCallbackPKCE(t *testing.T) {
defer tests.PrepareTestEnv(t)()
// Setup authentication source
gitlabName := "gitlab"
gitlab := addAuthSource(t, authSourcePayloadGitLabCustom(gitlabName))
// Create a user as if it had been previously been created by the authentication source.
userGitLabUserID := "5678"
userGitLab := &user_model.User{
Name: "gitlabuser",
Email: "gitlabuser@example.com",
Passwd: "gitlabuserpassword",
Type: user_model.UserTypeIndividual,
LoginType: auth_model.OAuth2,
LoginSource: gitlab.ID,
LoginName: userGitLabUserID,
}
defer createUser(context.Background(), t, userGitLab)()
// initial redirection (to generate the code_challenge)
session := emptyTestSession(t)
req := NewRequest(t, "GET", fmt.Sprintf("/user/oauth2/%s", gitlabName))
resp := session.MakeRequest(t, req, http.StatusTemporaryRedirect)
dest, err := url.Parse(resp.Header().Get("Location"))
assert.NoError(t, err)
assert.Equal(t, "S256", dest.Query().Get("code_challenge_method"))
codeChallenge := dest.Query().Get("code_challenge")
assert.NotEmpty(t, codeChallenge)
// callback (to check the initial code_challenge)
defer mockCompleteUserAuth(func(res http.ResponseWriter, req *http.Request) (goth.User, error) {
codeVerifier := req.URL.Query().Get("code_verifier")
assert.NotEmpty(t, codeVerifier)
assert.Greater(t, len(codeVerifier), 40, codeVerifier)
sha2 := sha256.New()
io.WriteString(sha2, codeVerifier)
assert.Equal(t, codeChallenge, base64.RawURLEncoding.EncodeToString(sha2.Sum(nil)))
return goth.User{
Provider: gitlabName,
UserID: userGitLabUserID,
Email: userGitLab.Email,
}, nil
})()
req = NewRequest(t, "GET", fmt.Sprintf("/user/oauth2/%s/callback?code=XYZ&state=XYZ", gitlabName))
resp = session.MakeRequest(t, req, http.StatusSeeOther)
assert.Equal(t, "/", test.RedirectURL(resp))
unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: userGitLab.ID})
}
func TestSignInOAuthCallbackRedirectToEscaping(t *testing.T) {
defer tests.PrepareTestEnv(t)()