authenticate: POC for supporting alternative OIDC redirect URLs

authenticate/authenticate.go

@@ -108,7 +108,7 @@ func (a *Authenticate) updateProvider(cfg *config.Config) error {
 	// configure our identity provider
 	provider, err := identity.NewAuthenticator(
 		oauth.Options{
-			RedirectURL:     redirectURL,
+			RedirectURL:     redirectURL.String(),
 			ProviderName:    cfg.Options.Provider,
 			ProviderURL:     cfg.Options.ProviderURL,
 			ClientID:        cfg.Options.ClientID,

authenticate/handlers.go

@@ -23,6 +23,7 @@ import (
 	"github.com/pomerium/pomerium/internal/httputil"
 	"github.com/pomerium/pomerium/internal/identity"
 	"github.com/pomerium/pomerium/internal/identity/manager"
+	"github.com/pomerium/pomerium/internal/identity/oauth"
 	"github.com/pomerium/pomerium/internal/identity/oidc"
 	"github.com/pomerium/pomerium/internal/log"
 	"github.com/pomerium/pomerium/internal/middleware"
@@ -56,7 +57,6 @@ func (a *Authenticate) Mount(r *mux.Router) {
 			csrf.Path("/"),
 			csrf.UnsafePaths(
 				[]string{
-					"/oauth2/callback",    // rfc6749#section-10.12 accepts GET
 					"/.pomerium/sign_out", // https://openid.net/specs/openid-connect-frontchannel-1_0.html
 				}),
 			csrf.FormValueName("state"), // rfc6749#section-10.12
@@ -306,13 +306,16 @@ func (a *Authenticate) reauthenticateOrFail(w http.ResponseWriter, r *http.Reque
 	}
 	state.sessionStore.ClearSession(w, r)
 	redirectURL := state.redirectURL.ResolveReference(r.URL)
-	nonce := csrf.Token(r)
-	now := time.Now().Unix()
-	b := []byte(fmt.Sprintf("%s|%d|", nonce, now))
-	enc := cryptutil.Encrypt(state.cookieCipher, []byte(redirectURL.String()), b)
-	b = append(b, enc...)
-	encodedState := base64.URLEncoding.EncodeToString(b)
-	signinURL, err := a.provider.Load().GetSignInURL(encodedState)
+
+	if rawOAuthRedirectURI := r.FormValue(urlutil.QueryOAuthRedirectURI); rawOAuthRedirectURI != "" {
+		redirectURL, err = urlutil.ParseAndValidateURL(rawOAuthRedirectURI)
+		if err != nil {
+			return httputil.NewError(http.StatusInternalServerError, err)
+		}
+	}
+
+	oauthState := oauth.NewState(redirectURL.String()).Encode(state.cookieCipher)
+	signinURL, err := a.provider.Load().GetSignInURL(oauthState, redirectURL.String())
 	if err != nil {
 		return httputil.NewError(http.StatusInternalServerError,
 			fmt.Errorf("failed to get sign in url: %w", err))
@@ -370,34 +373,12 @@ func (a *Authenticate) getOAuthCallback(w http.ResponseWriter, r *http.Request)
 		return nil, fmt.Errorf("error redeeming authenticate code: %w", err)
 	}
 
-	// state includes a csrf nonce (validated by middleware) and redirect uri
-	bytes, err := base64.URLEncoding.DecodeString(r.FormValue("state"))
-	if err != nil {
-		return nil, httputil.NewError(http.StatusBadRequest, fmt.Errorf("bad bytes: %w", err))
-	}
-
-	// split state into concat'd components
-	// (nonce|timestamp|redirect_url|encrypted_data(redirect_url)+mac(nonce,ts))
-	statePayload := strings.SplitN(string(bytes), "|", 3)
-	if len(statePayload) != 3 {
-		return nil, httputil.NewError(http.StatusBadRequest, fmt.Errorf("state malformed, size: %d", len(statePayload)))
-	}
-
-	// verify that the returned timestamp is valid
-	if err := cryptutil.ValidTimestamp(statePayload[1]); err != nil {
-		return nil, httputil.NewError(http.StatusBadRequest, err)
-	}
-
-	// Use our AEAD construct to enforce secrecy and authenticity:
-	// mac: to validate the nonce again, and above timestamp
-	// decrypt: to prevent leaking 'redirect_uri' to IdP or logs
-	b := []byte(fmt.Sprint(statePayload[0], "|", statePayload[1], "|"))
-	redirectString, err := cryptutil.Decrypt(state.cookieCipher, []byte(statePayload[2]), b)
+	oauthState, err := oauth.DecodeState(state.cookieCipher, r.FormValue("state"))
 	if err != nil {
 		return nil, httputil.NewError(http.StatusBadRequest, err)
 	}
 
-	redirectURL, err := urlutil.ParseAndValidateURL(string(redirectString))
+	redirectURL, err := urlutil.ParseAndValidateURL(oauthState.RedirectURL)
 	if err != nil {
 		return nil, httputil.NewError(http.StatusBadRequest, err)
 	}

authorize/check_response.go

@@ -38,6 +38,7 @@ func (a *Authorize) handleResultAllowed(
 func (a *Authorize) handleResultDenied(
 	ctx context.Context,
 	in *envoy_service_auth_v3.CheckRequest,
+	req *evaluator.Request,
 	result *evaluator.Result,
 	isForwardAuthVerify bool,
 	reasons criteria.Reasons,
@@ -49,7 +50,7 @@ func (a *Authorize) handleResultDenied(
 	case reasons.Has(criteria.ReasonUserUnauthenticated):
 		// when the user is unauthenticated it means they haven't
 		// logged in yet, so redirect to authenticate
-		return a.requireLoginResponse(ctx, in, isForwardAuthVerify)
+		return a.requireLoginResponse(ctx, in, req, isForwardAuthVerify)
 	case reasons.Has(criteria.ReasonDeviceUnauthenticated):
 		// when the user's device is unauthenticated it means they haven't
 		// registered a webauthn device yet, so redirect to the webauthn flow
@@ -141,19 +142,20 @@ func (a *Authorize) deniedResponse(
 func (a *Authorize) requireLoginResponse(
 	ctx context.Context,
 	in *envoy_service_auth_v3.CheckRequest,
+	req *evaluator.Request,
 	isForwardAuthVerify bool,
 ) (*envoy_service_auth_v3.CheckResponse, error) {
 	opts := a.currentOptions.Load()
 	state := a.state.Load()
-	authenticateURL, err := opts.GetAuthenticateURL()
-	if err != nil {
-		return nil, err
-	}
 
 	if !a.shouldRedirect(in) || isForwardAuthVerify {
 		return a.deniedResponse(ctx, in, http.StatusUnauthorized, http.StatusText(http.StatusUnauthorized), nil)
 	}
 
+	authenticateURL, err := opts.GetAuthenticateURL()
+	if err != nil {
+		return nil, err
+	}
 	signinURL := authenticateURL.ResolveReference(&url.URL{
 		Path: "/.pomerium/sign_in",
 	})
@@ -164,6 +166,17 @@ func (a *Authorize) requireLoginResponse(
 	checkRequestURL.Scheme = "https"
 
 	q.Set(urlutil.QueryRedirectURI, checkRequestURL.String())
+
+	// If an OAuthRedirectURL is explicitly set, pass that on the query string to
+	// override the default authenticate redirect url.
+	if req.Policy != nil && req.Policy.OAuthRedirectURL != "" {
+		u, err := urlutil.ParseAndValidateURL(req.Policy.OAuthRedirectURL)
+		if err != nil {
+			return nil, err
+		}
+		q.Set(urlutil.QueryOAuthRedirectURI, u.String())
+	}
+
 	signinURL.RawQuery = q.Encode()
 	redirectTo := urlutil.NewSignedURL(state.sharedKey, signinURL).String()
 

authorize/grpc.go

@@ -76,7 +76,7 @@ func (a *Authorize) Check(ctx context.Context, in *envoy_service_auth_v3.CheckRe
 
 	// if there's a deny, the result is denied using the deny reasons.
 	if res.Deny.Value {
-		return a.handleResultDenied(ctx, in, res, isForwardAuthVerify, res.Deny.Reasons)
+		return a.handleResultDenied(ctx, in, req, res, isForwardAuthVerify, res.Deny.Reasons)
 	}
 
 	// if there's an allow, the result is allowed.
@@ -85,7 +85,7 @@ func (a *Authorize) Check(ctx context.Context, in *envoy_service_auth_v3.CheckRe
 	}
 
 	// otherwise, the result is denied using the allow reasons.
-	return a.handleResultDenied(ctx, in, res, isForwardAuthVerify, res.Allow.Reasons)
+	return a.handleResultDenied(ctx, in, req, res, isForwardAuthVerify, res.Allow.Reasons)
 }
 
 func getForwardAuthURL(r *http.Request) *url.URL {

config/envoyconfig/routes.go

@@ -3,8 +3,10 @@ package envoyconfig
 import (
 	"encoding/json"
 	"fmt"
+	"net"
 	"net/url"
 	"sort"
+	"strconv"
 
 	envoy_config_core_v3 "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
 	envoy_config_route_v3 "github.com/envoyproxy/go-control-plane/envoy/config/route/v3"
@@ -17,6 +19,7 @@ import (
 
 	"github.com/pomerium/pomerium/config"
 	"github.com/pomerium/pomerium/internal/httputil"
+	"github.com/pomerium/pomerium/internal/identity/oauth"
 	"github.com/pomerium/pomerium/internal/urlutil"
 )
 
@@ -268,6 +271,14 @@ func (b *Builder) buildPolicyRoutes(options *config.Options, domain string) ([]*
 			continue
 		}
 
+		if policy.OAuthRedirectURL != "" {
+			oauthRedirectURLRoute, err := b.buildOAuthRedirectURLRoute(options, policy.OAuthRedirectURL)
+			if err != nil {
+				return nil, err
+			}
+			routes = append(routes, oauthRedirectURLRoute)
+		}
+
 		match := mkRouteMatch(&policy)
 		envoyRoute := &envoy_config_route_v3.Route{
 			Name:                   fmt.Sprintf("policy-%d", i),
@@ -446,6 +457,69 @@ func (b *Builder) buildPolicyRouteRouteAction(options *config.Options, policy *c
 	return action, nil
 }
 
+func (b *Builder) buildOAuthRedirectURLRoute(options *config.Options, rawOAuthRedirectURL string) (*envoy_config_route_v3.Route, error) {
+	oauthRedirectURL, err := urlutil.ParseAndValidateURL(rawOAuthRedirectURL)
+	if err != nil {
+		return nil, err
+	}
+
+	envoyRedirect, err := b.buildAuthenticateCallbackRouteRedirectAction(options)
+	if err != nil {
+		return nil, err
+	}
+
+	envoyRoute := &envoy_config_route_v3.Route{
+		Action: &envoy_config_route_v3.Route_Redirect{
+			Redirect: envoyRedirect,
+		},
+		Match: &envoy_config_route_v3.RouteMatch{
+			PathSpecifier: &envoy_config_route_v3.RouteMatch_Path{
+				Path: oauthRedirectURL.Path,
+			},
+			QueryParameters: []*envoy_config_route_v3.QueryParameterMatcher{
+				{Name: "state", QueryParameterMatchSpecifier: &envoy_config_route_v3.QueryParameterMatcher_StringMatch{
+					StringMatch: &envoy_type_matcher_v3.StringMatcher{
+						MatchPattern: &envoy_type_matcher_v3.StringMatcher_Prefix{
+							Prefix: oauth.StatePrefix,
+						},
+					},
+				}},
+			},
+		},
+		TypedPerFilterConfig: map[string]*any.Any{
+			"envoy.filters.http.ext_authz": disableExtAuthz,
+		},
+	}
+	return envoyRoute, nil
+}
+
+func (b *Builder) buildAuthenticateCallbackRouteRedirectAction(options *config.Options) (*envoy_config_route_v3.RedirectAction, error) {
+	authenticateURL, err := options.GetAuthenticateURL()
+	if err != nil {
+		return nil, err
+	}
+
+	authenticateURL = authenticateURL.ResolveReference(&url.URL{
+		Path: options.AuthenticateCallbackPath,
+	})
+
+	redirect := &envoy_config_route_v3.RedirectAction{}
+	if host, rawPort, err := net.SplitHostPort(authenticateURL.Host); err == nil {
+		if port, err := strconv.ParseUint(rawPort, 10, 32); err == nil {
+			redirect.HostRedirect = host
+			redirect.PortRedirect = uint32(port)
+		} else {
+			return nil, fmt.Errorf("invalid port in authenticate URL")
+		}
+	}
+	redirect.PathRewriteSpecifier = &envoy_config_route_v3.RedirectAction_PathRedirect{
+		PathRedirect: authenticateURL.Path,
+	}
+	redirect.ResponseCode = envoy_config_route_v3.RedirectAction_FOUND
+
+	return redirect, nil
+}
+
 func mkEnvoyHeader(k, v string) *envoy_config_core_v3.HeaderValueOption {
 	return &envoy_config_core_v3.HeaderValueOption{
 		Header: &envoy_config_core_v3.HeaderValue{

config/options.go

@@ -899,7 +899,7 @@ func (o *Options) GetOauthOptions() (oauth.Options, error) {
 		Path: o.AuthenticateCallbackPath,
 	})
 	return oauth.Options{
-		RedirectURL:    redirectURL,
+		RedirectURL:    redirectURL.String(),
 		ProviderName:   o.Provider,
 		ProviderURL:    o.ProviderURL,
 		ClientID:       o.ClientID,

config/policy.go

@@ -162,6 +162,9 @@ type Policy struct {
 	// SetResponseHeaders sets response headers.
 	SetResponseHeaders map[string]string `mapstructure:"set_response_headers" yaml:"set_response_headers,omitempty"`
 
+	// OAuthRedirectURL overrides the default authenticate redirect URL for this route.
+	OAuthRedirectURL string `mapstructure:"oauth_redirect_url" yaml:"oauth_redirect_url,omitempty"`
+
 	Policy *PPLPolicy `mapstructure:"policy" yaml:"policy,omitempty" json:"policy,omitempty"`
 }
 

internal/identity/oauth/github/github.go

@@ -78,7 +78,7 @@ func New(ctx context.Context, o *oauth.Options) (*Provider, error) {
 		ClientID:     o.ClientID,
 		ClientSecret: o.ClientSecret,
 		Scopes:       o.Scopes,
-		RedirectURL:  o.RedirectURL.String(),
+		RedirectURL:  o.RedirectURL,
 		Endpoint: oauth2.Endpoint{
 			AuthURL:  urlutil.Join(o.ProviderURL, authURL),
 			TokenURL: urlutil.Join(o.ProviderURL, tokenURL),
@@ -241,8 +241,10 @@ func (p *Provider) Revoke(ctx context.Context, token *oauth2.Token) error {
 
 // GetSignInURL returns a URL to OAuth 2.0 provider's consent page
 // that asks for permissions for the required scopes explicitly.
-func (p *Provider) GetSignInURL(state string) (string, error) {
-	return p.Oauth.AuthCodeURL(state, oauth2.AccessTypeOffline), nil
+func (p *Provider) GetSignInURL(state, redirectURL string) (string, error) {
+	oa := *p.Oauth
+	oa.RedirectURL = redirectURL
+	return oa.AuthCodeURL(state, oauth2.AccessTypeOffline), nil
 }
 
 // LogOut is not implemented by github.

internal/identity/oauth/options.go

@@ -3,8 +3,6 @@
 // authorization with Bearer JWT.
 package oauth
 
-import "net/url"
-
 // Options contains the fields required for an OAuth 2.0 (inc. OIDC) auth flow.
 //
 // https://tools.ietf.org/html/rfc6749
@@ -22,7 +20,7 @@ type Options struct {
 	ClientSecret string
 	// RedirectURL is the URL to redirect users going through
 	// the OAuth flow, after the resource owner's URLs.
-	RedirectURL *url.URL
+	RedirectURL string
 	// Scope specifies optional requested permissions.
 	Scopes []string
 

internal/identity/oauth/state.go

@@ -0,0 +1,80 @@
+package oauth
+
+import (
+	"bytes"
+	"crypto/cipher"
+	"encoding/base64"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/google/uuid"
+
+	"github.com/pomerium/pomerium/pkg/cryptutil"
+)
+
+// StatePrefix is the prefix used to indicate the state is via pomerium.
+const StatePrefix = "POMERIUM-"
+
+// State is the state in the oauth query string.
+type State struct {
+	Nonce       string
+	Timestamp   time.Time
+	RedirectURL string
+}
+
+// NewState creates a new State.
+func NewState(redirectURL string) *State {
+	return &State{
+		Nonce:       uuid.NewString(),
+		Timestamp:   time.Now(),
+		RedirectURL: redirectURL,
+	}
+}
+
+// DecodeState decodes state from a raw state string.
+func DecodeState(aead cipher.AEAD, rawState string) (*State, error) {
+	withoutPrefix := strings.TrimPrefix(rawState, StatePrefix)
+	rawStateBytes, err := base64.RawURLEncoding.DecodeString(withoutPrefix)
+	if err != nil {
+		return nil, fmt.Errorf("invalid state encoding: %w", err)
+	}
+
+	// split the state into its components
+	state := bytes.SplitN(rawStateBytes, []byte{'|'}, 3)
+	if len(state) != 3 {
+		return nil, fmt.Errorf("invalid state format")
+	}
+
+	// verify that the returned timestamp is valid
+	if err := cryptutil.ValidTimestamp(string(state[1])); err != nil {
+		return nil, fmt.Errorf("invalid state timestamp: %w", err)
+	}
+
+	nonce := string(state[0])
+	timestamp, err := strconv.ParseInt(string(state[1]), 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("invalid state timestamp: %w", err)
+	}
+
+	ad := []byte(fmt.Sprintf("%s|%d|", nonce, timestamp))
+	decrypted, err := cryptutil.Decrypt(aead, state[2], ad)
+	if err != nil {
+		return nil, fmt.Errorf("invalid state redirect URL: %w", err)
+	}
+
+	return &State{
+		Nonce:       nonce,
+		Timestamp:   time.Unix(timestamp, 0),
+		RedirectURL: string(decrypted),
+	}, nil
+}
+
+// Encode encodes the state.
+func (state *State) Encode(aead cipher.AEAD) string {
+	timestamp := state.Timestamp.Unix()
+	ad := []byte(fmt.Sprintf("%s|%d|", state.Nonce, timestamp))
+	encrypted := cryptutil.Encrypt(aead, []byte(state.RedirectURL), ad)
+	return StatePrefix + base64.RawURLEncoding.EncodeToString(append(ad, encrypted...))
+}

internal/identity/oidc/oidc.go

@@ -73,7 +73,7 @@ func New(ctx context.Context, o *oauth.Options, options ...Option) (*Provider, e
 				ClientSecret: o.ClientSecret,
 				Scopes:       o.Scopes,
 				Endpoint:     provider.Endpoint(),
-				RedirectURL:  o.RedirectURL.String(),
+				RedirectURL:  o.RedirectURL,
 			}
 		}),
 		WithGetProvider(func() (*go_oidc.Provider, error) {
@@ -103,11 +103,12 @@ func New(ctx context.Context, o *oauth.Options, options ...Option) (*Provider, e
 // always provide a non-empty string and validate that it matches the
 // the state query parameter on your redirect callback.
 // See http://tools.ietf.org/html/rfc6749#section-10.12 for more info.
-func (p *Provider) GetSignInURL(state string) (string, error) {
+func (p *Provider) GetSignInURL(state, redirectURL string) (string, error) {
 	oa, err := p.GetOauthConfig()
 	if err != nil {
 		return "", err
 	}
+	oa.RedirectURL = redirectURL
 
 	opts := defaultAuthCodeOptions
 	for k, v := range p.AuthCodeOptions {

internal/identity/providers.go

@@ -28,7 +28,7 @@ type Authenticator interface {
 	Authenticate(context.Context, string, identity.State) (*oauth2.Token, error)
 	Refresh(context.Context, *oauth2.Token, identity.State) (*oauth2.Token, error)
 	Revoke(context.Context, *oauth2.Token) error
-	GetSignInURL(state string) (string, error)
+	GetSignInURL(state, redirectURL string) (string, error)
 	Name() string
 	LogOut() (*url.URL, error)
 	UpdateUserInfo(ctx context.Context, t *oauth2.Token, v interface{}) error

internal/urlutil/query_params.go

@@ -10,6 +10,7 @@ const (
 	QueryEnrollmentToken    = "pomerium_enrollment_token" //nolint
 	QueryIsProgrammatic     = "pomerium_programmatic"
 	QueryForwardAuth        = "pomerium_forward_auth"
+	QueryOAuthRedirectURI   = "pomerium_oauth_redirect_uri"
 	QueryPomeriumJWT        = "pomerium_jwt"
 	QuerySession            = "pomerium_session"
 	QuerySessionEncrypted   = "pomerium_session_encrypted"