add(handler): Token Exchange rfc8693 in impersonation mode

Author: saxenautkarsh

handler/rfc8693/handler.go

@@ -0,0 +1,268 @@
+// Copyright © 2022 Ory Corp
+// SPDX-License-Identifier: Apache-2.0
+
+package rfc8693
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/ory/fosite"
+	"github.com/ory/fosite/compose"
+	"github.com/ory/fosite/handler/oauth2"
+	"github.com/ory/fosite/token/jwt"
+	"github.com/ory/x/errorsx"
+)
+
+// #nosec G101
+const (
+	tokenTypeIDToken = "urn:ietf:params:oauth:token-type:id_token"
+	tokenTypeAT      = "urn:ietf:params:oauth:token-type:access_token"
+)
+
+func TokenExchangeGrantFactory(config *compose.CommonStrategy, storage, strategy interface{}) interface{} {
+	return nil
+}
+
+type Handler struct {
+	Storage                  RFC8693Storage
+	Strategy                 ClientAuthenticationStrategy
+	ScopeStrategy            fosite.ScopeStrategy
+	AudienceMatchingStrategy fosite.AudienceMatchingStrategy
+	RefreshTokenStrategy     oauth2.RefreshTokenStrategy
+	RefreshTokenStorage      oauth2.RefreshTokenStorage
+	fosite.RefreshTokenScopesProvider
+
+	*oauth2.HandleHelper
+}
+
+type tokenExchangeParams struct {
+	subjectToken     string
+	subjectTokenType string
+}
+
+func parseRequestParameter(requester fosite.AccessRequester) (*tokenExchangeParams, error) {
+	form := requester.GetRequestForm()
+
+	// From https://tools.ietf.org/html/rfc8693#section-2.1:
+	//
+	//	subject_token
+	//		REQUIRED.  A security token that represents the identity of the
+	//		party on behalf of whom the request is being made.  Typically, the
+	//		subject of this token will be the subject of the security token
+	//		issued in response to the request.
+	subjectToken := form.Get("subject_token")
+	if subjectToken == "" {
+		return nil, errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("subject_token is missing"))
+	}
+
+	// From https://tools.ietf.org/html/rfc8693#section-2.1:
+	//
+	//	subject_token_type
+	//		REQUIRED.  An identifier, that indicates the type of the
+	// 		security token in the "subject_token" parameter.
+	subjectTokenType := form.Get("subject_token_type")
+	switch subjectTokenType {
+	case tokenTypeIDToken, tokenTypeAT:
+	default:
+		return nil, errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("unsupported or missing subject_token_type %s", subjectTokenType))
+	}
+
+	// From https://tools.ietf.org/html/rfc8693#section-2.1:
+	//
+	//	requested_token_type
+	//		OPTIONAL. An identifier, for the type of the requested security token.
+	// 		If the requested type is unspecified,
+	// 		the issued token type is at the discretion of the authorization server and
+	// 		may be dictated by knowledge of the requirements of the service or
+	// 		resource indicated by the resource or audience parameter.
+	requestedTokenType := form.Get("requested_token_type")
+	switch requestedTokenType {
+	case tokenTypeAT, "":
+	default:
+		return nil, errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("unsupported requested_token_type %s", requestedTokenType))
+	}
+
+	// From https://tools.ietf.org/html/rfc8693#section-2.1:
+	//
+	//	actor_token
+	//		OPTIONAL . A security token that represents the identity of the acting party.
+	//		Typically, this will be the party that is authorized to use the requested security
+	//		token and act on behalf of the subject.
+	actorToken := form.Get("actor_token")
+	if actorToken != "" {
+		return nil, errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("'actor_token' was provided but delegation is currently not supported."))
+	}
+
+	// From https://tools.ietf.org/html/rfc8693#section-2.1:
+	//
+	//	actor_token_type
+	//		An identifier, as described in Section 3, that indicates the type of the security token
+	//		in the actor_token parameter. This is REQUIRED when the actor_token parameter is present
+	//		in the request but MUST NOT be included otherwise.
+	actorTokenType := form.Get("actor_token_type")
+	if actorTokenType != "" {
+		return nil, errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("'actor_token_type' was provided but delegation is currently not supported."))
+	}
+
+	return &tokenExchangeParams{
+		subjectToken:     subjectToken,
+		subjectTokenType: subjectTokenType,
+	}, nil
+}
+
+func (c *Handler) HandleTokenEndpointRequest(ctx context.Context, requester fosite.AccessRequester) error {
+	if !c.CanHandleTokenEndpointRequest(requester) {
+		return errorsx.WithStack(fosite.ErrUnknownRequest)
+	}
+
+	client := requester.GetClient()
+	if client.GetID() == "" {
+		return errorsx.WithStack(fosite.ErrUnauthorizedClient.WithHint("unauthenticated client"))
+	}
+
+	// Check whether client is allowed to use token exchange.
+	if !client.GetGrantTypes().Has(string(fosite.GrantTypeTokenExchange)) {
+		return errorsx.WithStack(fosite.ErrUnauthorizedClient.WithHint("the client is not allowed to use token-exchange"))
+	}
+
+	// Get request parameter related token exchange.
+	params, err := parseRequestParameter(requester)
+	if err != nil {
+		return err
+	}
+
+	// Check and grant scope.
+	for _, scope := range requester.GetRequestedScopes() {
+		if !c.ScopeStrategy(client.GetScopes(), scope) {
+			return errorsx.WithStack(fosite.ErrInvalidScope.WithHintf("The OAuth 2.0 Client is not allowed to request scope '%s'.", scope))
+		}
+		requester.GrantScope(scope)
+	}
+
+	// Check and grant audience.
+	if err := c.AudienceMatchingStrategy(client.GetAudience(), requester.GetRequestedAudience()); err != nil {
+		return errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("audience not match: %v", err))
+	}
+	for _, audience := range requester.GetRequestedAudience() {
+		requester.GrantAudience(audience)
+	}
+
+	// Verify subject token.
+	switch params.subjectTokenType {
+	case tokenTypeIDToken:
+		claims := jwt.MapClaims{}
+		if _, err := jwt.ParseWithClaims(params.subjectToken, claims, c.keyFunc(ctx)); err != nil {
+			return errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("failed to verify JWT: %v", err))
+		}
+		subject, err := c.Storage.GetImpersonateSubject(ctx, claims, requester)
+		if err != nil {
+			return errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("not allowed to token exchange by jwt: %v", err))
+		}
+		requester.SetSession(&fosite.DefaultSession{
+			Subject: subject,
+		})
+		requester.GetSession().SetExpiresAt(fosite.AccessToken, time.Now().UTC().Add(c.Config.GetAccessTokenLifespan(ctx)))
+		return nil
+	case tokenTypeAT:
+		or, err := c.verifyAccessTokenAsSubjectToken(ctx, client.GetID(), params)
+		if err != nil {
+			return errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("not allowed to token exchange by at: %v", err))
+		}
+		requester.SetSession(or.GetSession().Clone())
+		// When the subject_type is AT, the expiration time is same with subject_token.
+		// Therefore, we don't need to set the expiresAt.
+		return nil
+	default:
+		return errorsx.WithStack(fosite.ErrInvalidRequest.WithHintf("unsupported subject_type %s", params.subjectTokenType))
+	}
+}
+
+func (c *Handler) PopulateTokenEndpointResponse(ctx context.Context, requester fosite.AccessRequester, responder fosite.AccessResponder) error {
+	if !c.CanHandleTokenEndpointRequest(requester) {
+		return errorsx.WithStack(fosite.ErrUnknownRequest)
+	}
+
+	if !requester.GetClient().GetGrantTypes().Has(string(fosite.GrantTypeTokenExchange)) {
+		return errorsx.WithStack(fosite.ErrUnauthorizedClient.WithHintf("The OAuth 2.0 Client is not allowed to use authorization grant '%s'.", fosite.GrantTypeTokenExchange))
+	}
+
+	atLifespan := fosite.GetEffectiveLifespan(requester.GetClient(), fosite.GrantTypeTokenExchange, fosite.AccessToken, c.Config.GetAccessTokenLifespan(ctx))
+
+	if err := c.IssueAccessToken(ctx, atLifespan, requester, responder); err != nil {
+		return err
+	}
+
+	if canIssueRefreshToken(ctx, c, requester) {
+		fmt.Println(requester)
+		refresh, refreshSignature, err := c.RefreshTokenStrategy.GenerateRefreshToken(ctx, requester)
+		if err != nil {
+			return errorsx.WithStack(fosite.ErrServerError.WithWrap(err).WithDebug(err.Error()))
+		}
+		if err := c.RefreshTokenStorage.CreateRefreshTokenSession(ctx, refreshSignature, requester); err != nil {
+			return errorsx.WithStack(fosite.ErrServerError.WithDebug(err.Error()))
+		}
+
+		responder.SetExtra("refresh_token", refresh)
+	}
+	return nil
+}
+
+func canIssueRefreshToken(ctx context.Context, c *Handler, requester fosite.Requester) bool {
+	scope := c.GetRefreshTokenScopes(ctx)
+	// Require one of the refresh token scopes, if set.
+	if len(scope) > 0 && !requester.GetGrantedScopes().HasOneOf(scope...) {
+		return false
+	}
+	// Do not issue a refresh token to clients that cannot use the refresh token grant type.
+	if !requester.GetClient().GetGrantTypes().Has("refresh_token") {
+		return false
+	}
+	return true
+}
+
+func (c *Handler) CanSkipClientAuth(requester fosite.AccessRequester) bool {
+	return c.Strategy.CanSkipClientAuth(requester)
+}
+
+func (c *Handler) keyFunc(ctx context.Context) jwt.Keyfunc {
+	return jwt.Keyfunc(func(t *jwt.Token) (interface{}, error) {
+		kid, ok := t.Header["kid"].(string)
+		if !ok {
+			return nil, errors.New("invalid kid")
+		}
+		iss, ok := t.Claims["iss"].(string)
+		if !ok {
+			return nil, errors.New("invalid iss")
+		}
+		return c.Storage.GetIDTokenPublicKey(ctx, iss, kid)
+	})
+}
+
+func (c *Handler) verifyAccessTokenAsSubjectToken(ctx context.Context, clientID string, params *tokenExchangeParams) (fosite.Requester, error) {
+	sig := c.HandleHelper.AccessTokenStrategy.AccessTokenSignature(ctx, params.subjectToken)
+	or, err := c.HandleHelper.AccessTokenStorage.GetAccessTokenSession(ctx, sig, nil)
+	if err != nil {
+		return nil, errorsx.WithStack(fosite.ErrRequestUnauthorized.WithWrap(err).WithDebug(err.Error()))
+	} else if err := c.AccessTokenStrategy.ValidateAccessToken(ctx, or, params.subjectToken); err != nil {
+		return nil, err
+	}
+
+	allowClientIDs, err := c.Storage.GetAllowedClientIDs(ctx, clientID)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, cid := range allowClientIDs {
+		if or.GetClient().GetID() == cid {
+			return or, nil
+		}
+	}
+	return nil, fmt.Errorf("this access_token is not allowed to use token exchange based on AT: original_client:%s, request_client:%s ", or.GetClient().GetID(), clientID)
+}
+
+func (c *Handler) CanHandleTokenEndpointRequest(requester fosite.AccessRequester) bool {
+	return requester.GetGrantTypes().ExactOne(string(fosite.GrantTypeTokenExchange))
+}